Hi Rudolf, I don't know that much about overlay keying colors. But I am pretty sure that the color at index 255 is the one used for representing transparency in B_CMAP8 bitmaps. It is never going to change. Confirmed. Wether this can be used for the overlay key color as well, I don't know for sure, but I would think it can. At least from your emails I had the impression that you're searching for the "magic" index. Sometimes earlier it was said, you cannot be sure about the index, since the color appears twice. This is not correct, while the color does appear twice, the magic index is always going to be 255. Best regards, -Stephan