hey mate, im only new to this, and i have he same prob... once or twice i have run out midway thru spraying, and its damn annoying, so now i tend to mix more paint than i need, just to be sure. and like the other guys have said, u can save it for later. last light i had some left over from painting disc brakes on my current build. i took the paint, added some bronze god and black (not much, just enuf to change the colour) and then i painted the center parts of the discs... and theres np way u can tell its the same colur!