Get number of system colors
Use GetDisplayColors function for this problem. This function returns number of bits on point of screen. For example, 16-65535, 8-256, 4-16.
function GetDisplayColors: integer; var tHDC: hdc; begin tHDC:=GetDC(0); Result:=GetDeviceCaps(tHDC, 12)*GetDeviceCaps(tHDC, 14); ReleaseDC(0, tHDC); end;