This is about the umpt time I'm posting this so please forgave me for repeating myself but have you considered using henna instead of chemical color? I am relaxed, with about 30 percent grey mostly in the front and henna colors, conditions and strengthens my hair like da bomb. Whenever some asks about color, I feel a moral obligation to at least mention henna as an option worth considering, especially since it is so good for relaxed hair. It is permanent red color that can be mixed with indigo ("black henna") for a wide range of colors from blue black to bright red.
I never used or even considered using chemical dyes so I can't help you there -- I refuse to use chemical dyes 'cause they're just too damaging and you have to keep applying them as new growth comes in, thus repeating the damaging cycle. Whereas with henna, I can apply every week to keep up with the color and not worry about damage; indeed, it conditions and glosses my hair as well as maintains my deep reddish brownish mahogany color on my black hairs and a reddish gold on my grey hair. The only time I lay off is two weeks before touchup and two weeks after, then I'm back to my weekly henna treatments such that I hardly use shampoo anymore. Just henna and apply deep conditioner after. Simple and beautiful! Indded, there some ladies on this board who specifically henna before and after touchups with great results so there may not even be reason to lay off at touchup time!
If you're interested, below are a couple of links to threads on this board for henna ladies as well as a link to the "henna for hair" websit that helped me understand that henna is an excellent colorant, conditioner and "secret weapon" for awesme relaxed hair. . . .
http://www.longhaircareforum.com/for...ad.php?t=87256
http://www.longhaircareforum.com/for...ighlight=henna
http://www.hennaforhair.com/