The Game Boy Pocket plays all original Game Boy (DMG) cartridges (black/gray label). It cannot natively play Game Boy Color (GBC) exclusive games (clear/black cartridges with a notch).
Requires a Game Boy Color → Pocket adapter (e.g., EMS "GB Converter"). Caveats:
For the best GBC experience, use a Game Boy Color, GBA, or GBA SP.