I have great success colouring my rhinestones with Promarkers. I bought a large bag of rhinestones from one of the pound shops in our town, only to find that some of them were a horrible colour and had two holes drilled through them. One day I wanted a particular colour rhinestone which I didn't have, so I painted glue over the top of a dingy one and sprinkled glitter over it before the glue dried. I was thrilled to bits with the result and I now see my not-so-good coloured rhinestones differently and went back to the pound shop and bought another bag! Hope you give this a try.