Are colored contacts safe to use? what are their long-term effects?

Maybe...: If they are prescribed by an eye care professional and are not novelty lenses, color contacts carry the same risks as clear lenses. Most important thing is regular hygiene.

Generally: Make sure the contacts are fitted by a professional contact lens fitter. Do not sleep in them-- the risk of infection goes up 30 fold. If the contacts are managed properly, there should be no long-term effects.