Aluminium doesn't corrode, because when exposed to atmosphere (air) it oxidizes (kinda rusts) pretty much straight away, preventing corrosion; it forms its own protective layer.
When you anodise aluminium, you use a electrical current and an acid (i seem to reacall) to increase the thickness of this protective layer. When this has been done the protective layer is porous, and can be dyed, any colour you want...
So you could have a pink FMIC, if that floats your boat
Not sure how much it would cost to do, and if they can just anodise the outside... i'd guess it wouldn't be cheap!
oh, and it shouldn't affect the performance of the FMIC at all (paint will, as it fills the small bits of the cooler with paint)