Don't spray it, have it annodised. Trouble is, it needs to be completely stripped (expensive unless you do it yourself and for that you really need to know inside out, literally ) and even then the process can affect the dimensions of critical things like regs etc. Not easy and not that cheap...
Hey mate, am getting Oli from Halloween to anno mine (when I get the money) so he may be able to do it... But I think he may only be able to do SP markers, not sure.