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XLS files use a 56 color palette (see Excel's Color Palette Explained). When using ExcelApplication's Workbook.Palette, ExcelWriter will throw an error if Palette.GetColor is called on an XLS file and the color doesn't exist in the palette. Customers are encouraged to use Palette.GetClosestColor to avoid calling for colors that don't exist in the palette. ExcelWriter will approximate which color from the 56 color palette to use.
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