There are questions that just make me cringe. This comes close, I can see a good working shotgun turned into a cosmetic mess.
And while I won't get mistaken for a gunsmith unless the light is really bad, my guess is getting this done professionally would cost about what a new Express or used WM would cost.
I suggest leaving it alone and getting another 870 with a classier finish.
I guess it could be blasted/polished like any other firearm and reblued. I don't recall ever refinishing a factory camoed gun before. I doubt that they are blued underneath the camo. I tend to agree with Dave on this one. I'd either just buy another 870 or maybe trade the camo for a blue one. George