I'd try to remove the spots before repainting, very carefully using a cotton bud and a little diluted solvent. You can re-paint when that's gone wrong!
Looking at my various colour charts of model paints, I'd start off by trying something like FS.x6495, which is about the palest un-tinted grey that's readily available. FS.x6622 is another possibility, but still be prepared to mix in a little white.
For an explanation of Federal Standard paint codes, see HERE. There are loads of other more recent colour conversion charts on modelling websites, but this is a very good place to start, and has stood the test of time well.