I agree, but if you want to evaluate mixture by the plug color you really need to cut the engine while it's running at the throttle / load condition you want to check, (ie full throttle etc). If you idle back to the dock, idling mixture is what you'll see.
Sounds like a carb problem, based on...
Possibly the most practical would be some anti slip paint.
Another, nicer, option would be to get some marine carpet cut to size and bound, then use snaps installed in the floating floor to secure, easy to take out to clean / dry. Stuck down carpet is going to get nasty quickly, especially if...