I've found GetDeviceCaps but it returns -1 for 24bit and 5120 for 256??

Declare Integer GetDC in win32api Integer
Declare Integer GetDeviceCaps in win32api Integer, Integer
?GetDeviceCaps(GetDC(0), 24)

>i mean the number of colours i.e 256 colours, 16 colours, high colours (16 bit), etc.