painting seat belts

I assume you meant painting the webbing material. If the purchase of new webbing is not possible, You could try SEM Color Coat paint. It is specifically designed for plastic and other interior materials. However, is buying the webbing and sewing up your own a possibility. I bought webbing, took the old ones apart carefully for patterns, and sewed up my own on the wife's sewing machine. I used the same type of thread, so I know they are PLENTY strong. I did the whole thing in one day.