Mgr, Kylash,
If the holsters are really latex you can use acrylic paints with rubber cement diluted with zippo lighter fluid 1:1. I used this on a crappy freddy mask in High school and it looked great afterwards. You just need regular rubber cement and some zippo lighter fluid, make sure its says 100% Naptha on it. Now add 1 part lighter fluid to 1 part rubber cement, stir in some acrylic paint and mix it well. It should be enough to give it color or else it will crack. Now brush it on or an alternative is always an airbrush. That's what I used. It usually takes 5-6 hours to dry so dont wait till halloween to paint the holsters. YMMV, if they are made of some other type of rubber.