any hairdressers?

i got my hair JS like 3 weeks ago, and need a color so bad(have black hair naturally so just to cover the grays) i have always just done the shades color because there aren't chemicals in it. Now i hear that after using shades you aren't EVER supposed to put chemicals in your hair and i really need to color again and don't know what is best. I would just need a single process, is the shades good or bad!