i just googled this and came up with these answers.
BTW what is this being used for
link aint working for me anymore so heres the raw link
Seems my other reply disappeared into cyber space. I am coloring the "glue" so we can easily see whether a joint is made properly or not, the solvent cement in Thailand is clear and colorless and the piping is light blue, making it very difficult to see whether the drunken plumbers have put glue in the joint or not.
Magic markers are solvent based. You might be able to take the inside felt from a marker and put it in the glue and let the marker dye infuse into the glue. I have never tried it so I don't know what the results will be but it would not be an expensive experiment to do.
Excellent thought Vyger, markers available in every stationary store locally, it is always a problem getting seemingly ordinary things in Thailand.