cclrImportant (ULONG)
More colors may be used in the bit map, but it is not necessary to assign them to the device palette. These additional colors may be mapped to the nearest colors available.
Zero (the default) means that all entries are important.
For a 24-bitcount standard format bit map, the cclrImportant colors are also listed in the color table following the BITMAPINFO2 structure.