you can also use coloured vinyl dye (which you can get in supercheap etc) if you need to match coloured bits... or colour your bits. Its not as accurate as the black stuff though, so if you use one application of red dye on your bits, they may turn into pink bits.
Make sure with any of these dyes that once you spray em on, you don't touch the plastic till they dry completely, as they turn soft while the solvent in the dye gets into them (which will leave fingerprints etc).