Title: 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;