Allow changing color in singleplayer

Preventing the player from changing skins in singleplayer (without enabling devmode) makes sense, because changing skins actually affects gameplay, and switching characters whenever a different ability is desired seems cheaty. But the skin color is different, as it's purely aesthetic. As such, if a player prefers to see their character in a different color, I see no reason why that and unlocking extras should be mutually exclusive.

Please let me know if you do have a good reason why this change shouldn't be made, or if I've made any mistakes in my implementation.