There is a big difference between backlights for the GBA vs. backlights for the DMG/MGB. The GBA backlight mod uses a TFT backlight color screen while the backlight panel for the DMG/MGB only uses LEDs and acrylic plastic, no actual LCD display. Check out this video from This Does not Comp below.
This Does Not Comp: I was getting nostalgic for GBA games, but hated the reflective screen on my original GBA. What to do? Mod it, of course!