I haven't tried using RIT dye on Glock sights myself, but I have friends who have tried it on other plastics. Their results were a bit all over the place. The white parts might soak it up, depending on what the material is, but I wouldn’t expect much to change with the black polymer. Just a heads up to keep an eye on the heat and soak time. Too much of either can warp or weaken the sight, and you definitely don’t want that. If you’re aiming for a fun pop of color, you could also think about using some model paint or even nail polish