This entry refers to the Game Boy Color portable console. Since the console was not region locked, this encompasses all regions in which the system was sold.
From Wikipedia:
First released in Japan on October 21, 1998, the Game Boy Color (abbreviated as GBC) added a color screen to a form factor slightly larger than the Game Boy Pocket. It also has double the processor speed, three times as much memory, and an infrared communications port. Technologically, it was likened to the 8-bit NES video game console from the 1980s although the Game Boy Color has a much larger color palette (56 simultaneous colors out of 32,768 possible).
A major component of the Game Boy Color is its near-universal backward compatibility (that is, a Game Boy Color is able to read older Game Boy cartridges and even play them in a selectable color palette) (The only Black & White Game Boy games known incompatible are Road Rash and Joshua: the Battle of Jericho). This backwards compatibility became a major feature of the Game Boy line, since it allowed each new launch to begin with a significantly larger library than any of its competitors. Some games written specifically for the Game Boy Color can be played on older model Game Boys, whereas others cannot.
Cartridges
Black: Dual Mode Game Boy Color games. Can be played on Game Boy, and Game Boy Color. Utilize Game Boy Colors enhanced pallet, but not expanded ram.
Clear: Will only play on Game Boy Color.