For DIBs loaded in memory, the color table can optionally consist of 2-byte entries - these entries constitute indexes to the currently realized palette instead of explicit RGB color definitions.

Microsoft does not disallow the presence of a valid alpha channel bit mask in and for 1bpp, 4bpp and 8bpp indexed color images, which indicates that the color table entries can also specify an alpha component using the 8.8.8.[0-8].[0-8] format via the RGBQUAD.rgbReserved member. However, some versions of Microsoft's