Hi, skins were added in the latest update as unlockable parts, so you need to go to the shop and unlock them with coins. Let me know if you've already done this and the issue occurs when starting a race.
I went back and checked after seeing your comment, thanks for the clarification! By the way, I bought this bundle as my students will absolutely love the idea of making classroom decisions based on which color of marble (or in this case motocross rider) wins a race :)
