What Guy said, they are game pieces not entries for the Games Workshop Golden Dragon competition.
Solid blocks of colour will be fine. If you really want to give a bit of zing then maybe a wash/drybrush to give lowlights/highlights.
A bottle or two of the Games Workshop washes, in green, brown and maybe black would be well worth it, as you will be able to use them on "normal" models as well.

Nothing fundamentally wrong with thinned down Jo Sonja or any cheapo water color paint either.
They will be handled so enamels may give more durability.
Above all, do it and have a go a figures, this is a great opportunity to experiment