I can't find a pic of the exact one I use and my camera doesn't work atm.
But I found this:
Remove the white stripes and the GBA logo, and stick a "Nintendo GAME BOY" logo in the bottom right corner.
I've had it ever since I bought my Gameboy Pocket (my first GB) about 10 years ago. I also used it for my Gameboy Color, then my Gameboy Advance SP, and now it holds my DS. I should wash it...