On that Ocean Turquoise one (yes, automotive paint - Gibson did this too), it's a regular maple neck with Brazilian rosewood fingerboard. The maple is darker just as the nitro lacquer has heavily yellowed - usually due to UV and/or nicotine, etc. The maple itself can darken with age and exposure, too.
On moving the thumb rest, if your bass has an original pickguard, I would STRONGLY encourage you not to drill any extra holes into it - just that part alone, if original, can be worth $500+ (I just anchor my thumb on the pickups or the edge of the neck) I have seen some people make their own thumb rests which used one of the existing pickguard screw holes and the hole for the chrome pickup cover on the E string side of the neck pickup. The idea is to make it as reversible as possible.