If you are having grey coverage issues I would definitely turn to Organic Color Systems. How their product works for grey coverage is very innovative. This color line does not contain PTDs, parabens, SLS, or Thioglycolates.

OCS uses an ingredient naturally derived from coconut to raise the hairs pH (in comparison to  the corrosive element- ammonia). The cuticle is softly swelled so the color particles may enter, the conditioning process of this color treatment then allows the cuticle to close. When the cuticle is able to close and the normal pH levels restored this allows for better color retention and less fading. Ammonia blasts the hair shaft open and damages the hair's Tyrosine (which is responsible for melanin product-color production).

It's true not all the ingredients are organic, but the fact they even have organic fruits, oils, and minerals used is remarkable to me. They also have over 60 color choices.

Check out this lady's full research on the color line. She even has photos of her color service with Organic Color Systems week by week. She is a 100% grey head client and notice had no fading! http://www.green-talk.com/2010/02/02/organic-color-systems-wash-those-grays-away-with-a-safer-hair-color/

Hope this helps.