Based on what I've read, the idea is that the clear receiver makes it legal to buy and import (for a business with a license to sell firearms). What you do after you buy the gun is your business as long as you don't wave it around in public. If you do attract attention to yourself, the gun (being painted) is nearly indistinguishable from the real thing and thusly will be treated as an illegal firearm. You WILL be charged with possession of an illegal firearm and any crimes committed will be tacked on with dangerous weapon charges.
In short, do what you want to your gun, but after you paint it, don't expect to be able to explain to the average police officer that your gun is legal (they'll pretty much treat it as real), although you shouldn't be taking your gun out into public to begin with.