When you turn the DS on, go to "System Settings" at the bottom of the screen (it is the picture of the DS), then go to "Personal Settings" (the picture of a person) and tap the color scheme (the top option, with the squares). Select a color, press A, press B(2), then press A again. Start the DS again, this time starting the game. Anytime you do a spine transfer, flip, roll, etc., there is a trail of color coming out of your board. That color will be the one you selected.