Paint should not affect RF propagation if it doesn't contain any metals. Some reds have significant iron oxide, some white's titanium oxides, etc. Keep in mind that even if it does affect RF propagation, it may be negligible at the short ranges most MURS applications operate at.
Can you test by covering the unit with tape and plastic then spray? If you notice a problem after it dries, strip it and regroup. If it works fine, strip it and paint a permanent coat.
~TG