A water based color would just "pearl" on the surface unless you got the mix percetly blended so that it would effectively dry as soon as it hit the grip- something laquer-based would be better. There is nothing for it to grip onto. You can usually create a transparent-like coat by just mixing a solid color with some clear, but in some instances the pigment with be too "rough". (I've done a lot of experimenting with creating gold and gunmetal tones, haha.) Black/brown would create a "muddy" look instead of deepening the color of the grips.