Returns whether or not the color is a custom color.

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 public boolean IsCustomColor{ get; }
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<p>Public ReadOnly Property IsCustomColor() As Boolean</p>

For .xls files a custom color is a color that is not part of Excel's default color palette. For .xlsx files, a custom color is any color that has not been retrieved from the legacy palette (through Palette.SetColorAt or Palette.GetColorAt), and is not a system color.