I understand that something has to be done in nifskope, but not really what - and any solutions I find via googling all seem to say that the Bound Bow doesn't recolor right, having a core that won't alter. Yet I see screenshots of people who have the thing correctly altered...

Possibly, If know nifscope, can find textures using in the BSEffectShaderProperty part pf the model. It lists 2 dds that vanilla bound weapon uses, both from effects folder. Have changed these for actors (using gimp) and changed the color of flames and other effects. So although haven't done for bound weapons I know it works on other things. Oh also an emmissive color there that may need to play around with to get a better look in the game. i am sure someone with more knowledge will chime in .. good fun with this.

Any idea on that last bit about the core of the bow?