I am not recommend you to repaint your retro glasses frames because it is difficult to do that and you are likely damage your eyeglasses lenses. So, you'd better buy another new pair of retro glasses frames. Now, with the development of e-commerce, you can get retro glasses frames from online optical shop with less amount of money. So, make the easy to buy new retro glasses frames.
If you want to repaint them, I would recommend fingernail polish. I have successfully painted my two pairs of glasses and It is quite an economical way to get new glasses. It is pretty tough and comes with a brush that is about the right size. If you paint the part around your lenses, you should probably take the lenses out first. If you don't like the color, you can easily remove it by nail polish remover.