[944boy]

It depends.... On the suede racing OMP steering wheel I bought, it is actual yellow leather sewn in. On some hardcore rally and other racing cars (non multi-million dollar cars) its bright electrical tape. On the carbon wheel you pictured, it could either be paper or plastic material embedded into the resin/clear. Or vinyl tape on the outside. But not having seen it in person I could not tell you. It could also be paint then cleared over.

For your leather wheel I don't know of an easy way to add the stripe that would look good.