At the character select screen push and hold down the left stick and tilt it either right, left, up or down. Depending on where you tilt it chooses your skin color.

Code	Effect
Hold down left stick and tilt left	Get Fourth skin.
Hold down left stick and tilt up	Get Original skin.
Hold down left stick and tilt right	Get Secondary skin.
Hold down left stick and tilt down	Get Third skin.