Kel-Tec sells replacement grips for the P-3AT for $34 (P-3AT grips) in black, green or gray. But with an affordable little pistol like this, why not have some fun. Order a grip and then paint it yourself. I am going to try this and see how well it works. Caution: use an appropriate paint! From all I have read, for the paint to last and not rub off, you need a duracoat paint. There are gunsmiths out there that will do this for you, but I found this dealer, Lauer Weaponry, that sells a turn-key system called Durocoat Shake 'N Spray for $29. Let me know if you have any experience with this product and I will make a post once I try it.
Lauer Weaponry's example video of how Shake 'N Spray works: example video
Gunsmith professional example of durocoat examples: Golden Loki