diff --git a/src/PhpSpreadsheet/Comment.php b/src/PhpSpreadsheet/Comment.php
index 31f76640..12fb0e22 100644
--- a/src/PhpSpreadsheet/Comment.php
+++ b/src/PhpSpreadsheet/Comment.php
@@ -3,6 +3,8 @@
 namespace PhpOffice\PhpSpreadsheet;
 
 use PhpOffice\PhpSpreadsheet\RichText\RichText;
+use PhpOffice\PhpSpreadsheet\Style\Alignment;
+use PhpOffice\PhpSpreadsheet\Style\Color;
 
 class Comment implements IComparable
 {
@@ -58,7 +60,7 @@ class Comment implements IComparable
     /**
      * Comment fill color.
      *
-     * @var Style\Color
+     * @var Color
      */
     private $fillColor;
 
@@ -77,8 +79,8 @@ class Comment implements IComparable
         // Initialise variables
         $this->author = 'Author';
         $this->text = new RichText();
-        $this->fillColor = new Style\Color('FFFFFFE1');
-        $this->alignment = Style\Alignment::HORIZONTAL_GENERAL;
+        $this->fillColor = new Color('FFFFFFE1');
+        $this->alignment = Alignment::HORIZONTAL_GENERAL;
     }
 
     /**
@@ -86,7 +88,7 @@ class Comment implements IComparable
      *
      * @return string
      */
-    public function getAuthor()
+    public function getAuthor(): string
     {
         return $this->author;
     }
@@ -98,7 +100,7 @@ class Comment implements IComparable
      *
      * @return $this
      */
-    public function setAuthor($author)
+    public function setAuthor(string $author)
     {
         $this->author = $author;
 
@@ -110,7 +112,7 @@ class Comment implements IComparable
      *
      * @return RichText
      */
-    public function getText()
+    public function getText(): RichText
     {
         return $this->text;
     }
@@ -118,11 +120,13 @@ class Comment implements IComparable
     /**
      * Set Rich text comment.
      *
+     * @param RichText $text
+     *
      * @return $this
      */
-    public function setText(RichText $pValue)
+    public function setText(RichText $text)
     {
-        $this->text = $pValue;
+        $this->text = $text;
 
         return $this;
     }
@@ -132,7 +136,7 @@ class Comment implements IComparable
      *
      * @return string
      */
-    public function getWidth()
+    public function getWidth(): string
     {
         return $this->width;
     }
@@ -140,11 +144,11 @@ class Comment implements IComparable
     /**
      * Set comment width (CSS style, i.e. XXpx or YYpt).
      *
-     * @param string $width
+     * @param string $width including units (px or pt)
      *
      * @return $this
      */
-    public function setWidth($width)
+    public function setWidth(string $width)
     {
         $this->width = $width;
 
@@ -156,7 +160,7 @@ class Comment implements IComparable
      *
      * @return string
      */
-    public function getHeight()
+    public function getHeight(): string
     {
         return $this->height;
     }
@@ -164,13 +168,13 @@ class Comment implements IComparable
     /**
      * Set comment height (CSS style, i.e. XXpx or YYpt).
      *
-     * @param string $value
+     * @param string $height including units (px or pt)
      *
      * @return $this
      */
-    public function setHeight($value)
+    public function setHeight(string $height)
     {
-        $this->height = $value;
+        $this->height = $height;
 
         return $this;
     }
@@ -180,7 +184,7 @@ class Comment implements IComparable
      *
      * @return string
      */
-    public function getMarginLeft()
+    public function getMarginLeft(): string
     {
         return $this->marginLeft;
     }
@@ -188,13 +192,13 @@ class Comment implements IComparable
     /**
      * Set left margin (CSS style, i.e. XXpx or YYpt).
      *
-     * @param string $value
+     * @param string $margin including units (px or pt)
      *
      * @return $this
      */
-    public function setMarginLeft($value)
+    public function setMarginLeft(string $margin)
     {
-        $this->marginLeft = $value;
+        $this->marginLeft = $margin;
 
         return $this;
     }
@@ -204,7 +208,7 @@ class Comment implements IComparable
      *
      * @return string
      */
-    public function getMarginTop()
+    public function getMarginTop(): string
     {
         return $this->marginTop;
     }
@@ -212,13 +216,13 @@ class Comment implements IComparable
     /**
      * Set top margin (CSS style, i.e. XXpx or YYpt).
      *
-     * @param string $value
+     * @param string $margin including units (px or pt)
      *
      * @return $this
      */
-    public function setMarginTop($value)
+    public function setMarginTop(string $margin)
     {
-        $this->marginTop = $value;
+        $this->marginTop = $margin;
 
         return $this;
     }
@@ -228,7 +232,7 @@ class Comment implements IComparable
      *
      * @return bool
      */
-    public function getVisible()
+    public function getVisible(): bool
     {
         return $this->visible;
     }
@@ -236,13 +240,27 @@ class Comment implements IComparable
     /**
      * Set comment default visibility.
      *
-     * @param bool $value
+     * @param bool $visibility
      *
      * @return $this
      */
-    public function setVisible($value)
+    public function setVisible(bool $visibility)
     {
-        $this->visible = $value;
+        $this->visible = $visibility;
+
+        return $this;
+    }
+
+    /**
+     * Set fill color.
+     *
+     * @param Color $color
+     *
+     * @return $this
+     */
+    public function setFillColor(Color $color)
+    {
+        $this->fillColor = $color;
 
         return $this;
     }
@@ -250,9 +268,9 @@ class Comment implements IComparable
     /**
      * Get fill color.
      *
-     * @return Style\Color
+     * @return Color
      */
-    public function getFillColor()
+    public function getFillColor(): Color
     {
         return $this->fillColor;
     }
@@ -260,11 +278,11 @@ class Comment implements IComparable
     /**
      * Set Alignment.
      *
-     * @param string $alignment see Style\Alignment::HORIZONTAL_*
+     * @param string $alignment see Alignment::HORIZONTAL_*
      *
      * @return $this
      */
-    public function setAlignment($alignment)
+    public function setAlignment(string $alignment): string
     {
         $this->alignment = $alignment;
 
diff --git a/src/PhpSpreadsheet/IOFactory.php b/src/PhpSpreadsheet/IOFactory.php
index ab04e969..f3ce6a30 100644
--- a/src/PhpSpreadsheet/IOFactory.php
+++ b/src/PhpSpreadsheet/IOFactory.php
@@ -3,6 +3,7 @@
 namespace PhpOffice\PhpSpreadsheet;
 
 use PhpOffice\PhpSpreadsheet\Shared\File;
+use PhpOffice\PhpSpreadsheet\Writer\IWriter;
 
 /**
  * Factory to create readers and writers easily.
@@ -41,7 +42,7 @@ abstract class IOFactory
      *
      * @return Writer\IWriter
      */
-    public static function createWriter(Spreadsheet $spreadsheet, $writerType)
+    public static function createWriter(Spreadsheet $spreadsheet, string $writerType): Writer\IWriter
     {
         if (!isset(self::$writers[$writerType])) {
             throw new Writer\Exception("No writer found for type $writerType");
@@ -60,7 +61,7 @@ abstract class IOFactory
      *
      * @return Reader\IReader
      */
-    public static function createReader($readerType)
+    public static function createReader(string $readerType): Reader\IReader
     {
         if (!isset(self::$readers[$readerType])) {
             throw new Reader\Exception("No reader found for type $readerType");
@@ -79,7 +80,7 @@ abstract class IOFactory
      *
      * @return Spreadsheet
      */
-    public static function load($pFilename)
+    public static function load(string $pFilename): Spreadsheet
     {
         $reader = self::createReaderForFile($pFilename);
 
@@ -93,7 +94,7 @@ abstract class IOFactory
      *
      * @return string
      */
-    public static function identify($pFilename)
+    public static function identify(string $pFilename): string
     {
         $reader = self::createReaderForFile($pFilename);
         $className = get_class($reader);
@@ -110,7 +111,7 @@ abstract class IOFactory
      *
      * @return Reader\IReader
      */
-    public static function createReaderForFile($filename)
+    public static function createReaderForFile(string $filename): Reader\IReader
     {
         File::assertFile($filename);
 
@@ -147,7 +148,7 @@ abstract class IOFactory
      *
      * @return null|string
      */
-    private static function getReaderTypeFromExtension($filename)
+    private static function getReaderTypeFromExtension(string $filename): ?string
     {
         $pathinfo = pathinfo($filename);
         if (!isset($pathinfo['extension'])) {
@@ -191,7 +192,7 @@ abstract class IOFactory
      * @param string $writerType
      * @param string $writerClass
      */
-    public static function registerWriter($writerType, $writerClass): void
+    public static function registerWriter(string $writerType, string $writerClass): void
     {
         if (!is_a($writerClass, Writer\IWriter::class, true)) {
             throw new Writer\Exception('Registered writers must implement ' . Writer\IWriter::class);
@@ -206,7 +207,7 @@ abstract class IOFactory
      * @param string $readerType
      * @param string $readerClass
      */
-    public static function registerReader($readerType, $readerClass): void
+    public static function registerReader(string $readerType, string $readerClass): void
     {
         if (!is_a($readerClass, Reader\IReader::class, true)) {
             throw new Reader\Exception('Registered readers must implement ' . Reader\IReader::class);
diff --git a/src/PhpSpreadsheet/Settings.php b/src/PhpSpreadsheet/Settings.php
index cfa50573..1b760578 100644
--- a/src/PhpSpreadsheet/Settings.php
+++ b/src/PhpSpreadsheet/Settings.php
@@ -63,7 +63,7 @@ class Settings
      *
      * @return bool Success or failure
      */
-    public static function setLocale($locale)
+    public static function setLocale(string $locale)
     {
         return Calculation::getInstance()->setLocale($locale);
     }
@@ -74,7 +74,7 @@ class Settings
      * @param string $rendererClass Class name of the chart renderer
      *    eg: PhpOffice\PhpSpreadsheet\Chart\Renderer\JpGraph
      */
-    public static function setChartRenderer($rendererClass): void
+    public static function setChartRenderer(string $rendererClass): void
     {
         if (!is_a($rendererClass, IRenderer::class, true)) {
             throw new Exception('Chart renderer must implement ' . IRenderer::class);
@@ -89,7 +89,7 @@ class Settings
      * @return null|string Class name of the chart renderer
      *    eg: PhpOffice\PhpSpreadsheet\Chart\Renderer\JpGraph
      */
-    public static function getChartRenderer()
+    public static function getChartRenderer(): string
     {
         return self::$chartRenderer;
     }
@@ -113,7 +113,7 @@ class Settings
      *
      * @return int Default options for libxml loader
      */
-    public static function getLibXmlLoaderOptions()
+    public static function getLibXmlLoaderOptions(): int
     {
         if (self::$libXmlLoaderOptions === null && defined('LIBXML_DTDLOAD')) {
             self::setLibXmlLoaderOptions(LIBXML_DTDLOAD | LIBXML_DTDATTR);
@@ -144,7 +144,7 @@ class Settings
      *
      * @return bool $state
      */
-    public static function getLibXmlDisableEntityLoader()
+    public static function getLibXmlDisableEntityLoader(): bool
     {
         return self::$libXmlDisableEntityLoader;
     }
@@ -162,7 +162,7 @@ class Settings
      *
      * @return CacheInterface
      */
-    public static function getCache()
+    public static function getCache(): CacheInterface
     {
         if (!self::$cache) {
             self::$cache = new Memory();
diff --git a/src/PhpSpreadsheet/Style/Color.php b/src/PhpSpreadsheet/Style/Color.php
index d8ba08b2..78c860fb 100644
--- a/src/PhpSpreadsheet/Style/Color.php
+++ b/src/PhpSpreadsheet/Style/Color.php
@@ -27,6 +27,9 @@ class Color extends Supervisor
     const COLOR_YELLOW = 'FFFFFF00';
     const COLOR_DARKYELLOW = 'FF808000';
 
+    const VALIDATE_ARGB = '/^[A-F0-9]{8}$/i';
+    const VALIDATE_RGB = '/^[A-F0-9]{6}$/i';
+
     /**
      * Indexed colors array.
      *
@@ -44,7 +47,7 @@ class Color extends Supervisor
     /**
      * Create a new Color.
      *
-     * @param string $pARGB ARGB value for the colour
+     * @param string $colorValue ARGB value for the colour, or named colour
      * @param bool $isSupervisor Flag indicating if this is a supervisor or not
      *                                    Leave this value at default unless you understand exactly what
      *                                        its ramifications are
@@ -52,14 +55,14 @@ class Color extends Supervisor
      *                                    Leave this value at default unless you understand exactly what
      *                                        its ramifications are
      */
-    public function __construct($pARGB = self::COLOR_BLACK, $isSupervisor = false, $isConditional = false)
+    public function __construct($colorValue = self::COLOR_BLACK, $isSupervisor = false, $isConditional = false)
     {
         //    Supervisor?
         parent::__construct($isSupervisor);
 
         //    Initialise values
         if (!$isConditional) {
-            $this->argb = $pARGB;
+            $this->argb = $this->setARGB($colorValue);
         }
     }
 
@@ -125,7 +128,7 @@ class Color extends Supervisor
      *
      * @return string
      */
-    public function getARGB()
+    public function getARGB(): ?string
     {
         if ($this->isSupervisor) {
             return $this->getSharedComponent()->getARGB();
@@ -134,23 +137,32 @@ class Color extends Supervisor
         return $this->argb;
     }
 
+    private function validateARGB(string $colorValue): bool
+    {
+        return in_array(ucfirst($colorValue), self::NAMED_COLORS) ||
+            preg_match(self::VALIDATE_ARGB, $colorValue);
+    }
+
     /**
      * Set ARGB.
      *
-     * @param string $pValue see self::COLOR_*
+     * @param string $colorValue  ARGB value, or a named color
      *
      * @return $this
      */
-    public function setARGB($pValue)
+    public function setARGB(string $colorValue)
     {
-        if ($pValue == '') {
-            $pValue = self::COLOR_BLACK;
+        if ($colorValue == '') {
+            $colorValue = self::COLOR_BLACK;
+        } elseif (!$this->validateARGB($colorValue)) {
+            return $this;
         }
+
         if ($this->isSupervisor) {
-            $styleArray = $this->getStyleArray(['argb' => $pValue]);
+            $styleArray = $this->getStyleArray(['argb' => $colorValue]);
             $this->getActiveSheet()->getStyle($this->getSelectedCells())->applyFromArray($styleArray);
         } else {
-            $this->argb = $pValue;
+            $this->argb = $colorValue;
         }
 
         return $this;
@@ -161,7 +173,7 @@ class Color extends Supervisor
      *
      * @return string
      */
-    public function getRGB()
+    public function getRGB(): ?string
     {
         if ($this->isSupervisor) {
             return $this->getSharedComponent()->getRGB();
@@ -170,23 +182,32 @@ class Color extends Supervisor
         return substr($this->argb, 2);
     }
 
+    private function validateRGB(string $colorValue): bool
+    {
+        return in_array(ucfirst($colorValue), self::NAMED_COLORS) ||
+            preg_match(self::VALIDATE_RGB, $colorValue);
+    }
+
     /**
      * Set RGB.
      *
-     * @param string $pValue RGB value
+     * @param string $colorValue RGB value, or a named color
      *
      * @return $this
      */
-    public function setRGB($pValue)
+    public function setRGB(string $colorValue)
     {
-        if ($pValue == '') {
-            $pValue = '000000';
+        if ($colorValue == '') {
+            $colorValue = '000000';
+        } elseif (!$this->validateRGB($colorValue)) {
+            return $this;
         }
+
         if ($this->isSupervisor) {
-            $styleArray = $this->getStyleArray(['argb' => 'FF' . $pValue]);
+            $styleArray = $this->getStyleArray(['argb' => 'FF' . $colorValue]);
             $this->getActiveSheet()->getStyle($this->getSelectedCells())->applyFromArray($styleArray);
         } else {
-            $this->argb = 'FF' . $pValue;
+            $this->argb = 'FF' . $colorValue;
         }
 
         return $this;
diff --git a/src/PhpSpreadsheet/Style/Style.php b/src/PhpSpreadsheet/Style/Style.php
index 533a7c38..012677f4 100644
--- a/src/PhpSpreadsheet/Style/Style.php
+++ b/src/PhpSpreadsheet/Style/Style.php
@@ -110,7 +110,7 @@ class Style extends Supervisor
      *
      * @return Style
      */
-    public function getSharedComponent()
+    public function getSharedComponent(): Style
     {
         $activeSheet = $this->getActiveSheet();
         $selectedCell = $this->getActiveCell(); // e.g. 'A1'