Welcome to the forum. I don't think you need to buy anything. Just cut a small patch from a white plastic aspirin bottle, superglue it to the sight, and use an exacto knife to shave the overlap down to the face of the blade. Some people just hit the rear face of the front sight with some refrigerator touch-up paint. Seems to me most ramp sights have colored inserts rather than glue-ons, so I would probably go with paint. In fact I did just that with the ramp front sight of a 649.
I was faced with the same issue on my Model 15-2. I used regular white-out correction fluid and it worked perfectly. It tends to chip off over time but a quick dab from the bottle and it's set to go for another few months.
Ditto on the White Out. Check out Finger Nail Polish too, Comes in all sorts of vibrant colors these days and you can change the color of your nails, er front sight, with the application of a little bit of nail polish remover.