Это работает, возвращая PIL-совместимую палитру:
import ctypes, win32gui
def getSystemPalette():
hwnd = win32gui.GetDesktopWindow()
hwndDC = win32gui.GetWindowDC(hwnd)
buff = ctypes.c_buffer("0"*(256*4)) #R, G, B, and flags
ctypes.windll.gdi32.GetSystemPaletteEntries(hwndDC, 0, 256, buff)
win32gui.ReleaseDC(hwnd, hwndDC)
#ignore every 4th entry which is the flags
res = [ord(x) for i,x in enumerate(buff) if i%4 != 3]
return res