Bibin said:
Every game that runs with color in it at all? It's using the double clock speed.
What? No no no no no, Bibin I am disappointed in you.
Any Gameboy game could run on a CGB.
With the CGB, many games added color support. Many even before the CGB was actually released.
A simple check to see if a CGB was being used. If it was, enable the colors. If not, then simply don't.
The Double Speed Mode was not required to be used for colors.
Many, games took advantage of the MBC5 Bank controller, which was necessary to run at the Double Speed Mode.
MBC5 Games could still be used on a Gameboy, if they were made to, but of course, it would be impossible to use the Double Speed Mode while being played on a normal Gameboy.
Commonly, "High Color" images were displayed with the help of the Double Speed Mode.
While each Background Tile could only use 4 colors, some fancy ASM that worked as the Tiles were drawn could allow about 2000 colors to be used at once.
(Though, no more than 80 colors per scanline)
It's about the easiest way to identify a game using the Double Speed Mode, looking for highly-detailed images.