If you wish to play your old Nintendo Game Boy Color games on your Nintendo Game Boy Advance, you're in luck. The Nintendo Game Boy Advance, often shortened to simply GBA, is backward-compatible with most Game Boy Color (GBC) and Game Boy games. This applies only to the original GBA and the GBA SP. If you own a GBA Micro, you will not be able to play GBC games on your system.
Insert your GBC game cartridge into the cartridge slot of your GBA or GBA SP.
Turn the power on by sliding the power switch to the "On" position.
Play the GBC game as if you were playing it on your Game Boy Color.
You can change the colour scheme of the game by pressing the D-pad or buttons when the "Game Boy Advance" screen shows up. You can have the GBC game fill up the whole screen or play it at its intended dimensions by toggling with the "L" and "R" buttons.