Cotton,
In the past I have used fingernail polish to thwart that very thing. Brush and clean up the sight real good. Leave no paint residue(bluing is ok). I use alcohol. Then 2 coats of the fingernail polish color of your choice. Let dry very well between coats. Then top off with 1 coat clear finger nail polish to seal the deal. Keep your coats VERY thin and be patient with the drying between. I've experimented with # of coats and found that less is more. Put too many layers and it all peels off in one thick layer. If you accidentally glop or otherwise make one of your coats too thick, take it all off and start over. Again, patience has paid off for me here. I have gotten a whole deer season out of one set up as described above, but I don't always unholster my revolver when I get home from the field unless it's been a damp or snowy day, or unless I won't be hunting for a few days after.
Give it a shot. I've had fair luck with it. Better than paint anyway.
Renster