Fix#3093. PR #2595 added the ability for Xlsx Reader to accept a custom color palette. With no examples other than the one at hand, which included a full complement of 64 colors, that PR required 64 colors in the palette. It turns out that Mac Numbers exports to Excel with a palette with less than 64 colors. So, with an example of that at hand, relax the original restriction and accept a palette of any size.