Transparency on a panel

I'm sure this question has been beaten like a horse, but I still can't find a definite answer. What exactly flags a pixel for transparency on a panel?At first I thought it was whatever color is at Index 0 on the 8-bit image palette. Now everything I read says it is whatever is black (0,0,0). However, in any bitmaps I make, even if I have a 0,0,0 palette entry, it will NOT be the transparent pixels UNLESS it it is Index 0. Now, to make it more complex, I looked at some of the default MS panels and their transparent pixels aren't always Index 0. Now that I've found evidence to support either theory, which one is actually correct? It's still quite a pain for me to make a good panel bitmap.I wish it were possible to use 24 bit panels!Enrique