If we are printing from negatives or transparencies in a darkroom we will at some time get dust spots or hair, no matter how careful we are making sure that the negative is blemish free. Spotting inks are (in the UK) almost bank loan prices, but a good alternative for colour as well as monochrome is to use inks from an inkjet printer. They are water soluble and will do the task just as efficiently as those dyes sold especially for the purpose and at a mere fraction of the price..The colour variations possible are almost infinite.