Game Boy Color hardware

In-game reset:
Press A + B + Start + Select during game play to reset most Game Boy and Game Boy Color games.

Invert colors:
Press Right + B at the Game Boy logo to reverse the screen and sprite colors.
This may make the game easier to see in dim light.

Other colors:
Other color schemes (as stated in the manual) may be selected at the Game Boy logo by pressing the following combinations.
Note: This only affects regular and not color Game Boy games.

Up: Bright Red
Up + A: Red
Up + B: Dark Red
Down: Pastel
Down + A: Orange
Down + B: Gold
Left: Bright Blue
Left + A: Dark Blue
Left + B: Grey
Right: Bright Green
Right + A: Dark Green
Right + B: Invert Colors