I need to stop collecting these.
The purple and black GBAs came from eBay, while the yellow version (it looks orange in the photo, but it’s really banana yellow) is from Retro Modding. Like GB modders Deadpan Robot (formerly Gameboy Mods), Retro Modding take used GBAs and refurbish them with a variety of third-party shells and enhancements.
I was very pleased with Retro Modding. In addition to providing great service and doing an excellent job of modifying the GBA - for considerably less than the current prices on eBay - they threw in a neat case and a bunch of stickers.
Aspiring backlit GBA owners should note that a triwing screwdriver may turn out to be an essential purchase. Two of these three handhelds have required adjustments to the voltage potentiometer inside the console in order to fix graphical glitches on the screen. The purple unit displayed flickering colors, whilst the yellow unit was noticably interlaced. There’s a video here that demonstrates where to insert a screwdriver if you don’t mind poking a hole in the sticker on the back of the device, but a triwing screwdriver will allow you to open it up and avoid the hole.
The approach that’s worked best for me is to make small adjustments of around a quarter-turn, testing out the console with each change. It’s a little laborious, as each test requires reassembling the console enough to be able to re-insert the cartridge and batteries, but I’ve seen numerous (unsubstantiated) reports that turning it too far can damage the screen. The purple unit was particularly troublesome to get right because it would work well for a day or so before the flickering re-appeared.