The M36 front sight is integral with the barrel, so it is non removable and non replaceable. Other than painting it, you could cut a notch in it and use red (or other colored) plastic inserts. I would however NOT recommend that on a J-frame since the front sight is so thin. It would more than likely fall out of the notch after a while. If you must have the front sight colored, I would use Testor's international orange colored paint. It lasts for a long time, is highly visible, and is easily removable if so desired.
Regards,
Chief38