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 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.

Background Combination:

Green, Blue None
Brown Up
Red Up + A
Dark Brown Up + B
Blue Left
Dark Blue Left + A
Green Left + B
Yellow, Red, Blue Down
Yellow, Red Down + A
Yellow Down + B
Green, Red Right
Green, Blue Right + A
Invert Right + B

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