blue roots

Hey guys! I've been coloring my naturally light brown hair to a very dark brown for a few months,almost black.Reacently I decided to go totally black and I used Feria. I loved the result, my hair is really black except of the roots very near the scalp which turned kinda bluish-violet.Anybody know the reason and what should I do to fix it? I don't want to color my hair again bc it is already enough saturated with color, just want to know what  to do to prevent this problem by the next touch up.

Also I've been thinking of going dark chocolate brown somewhere in the future. My question is: should I stop coloring my hair for a few months before, just to make it an easier job for the colorist?I don't know if it would make any difference... Oh and one more thing! If I take a picture of a certain color to the salon, can they produce the exact shade on me?

Thanx guys!

Going lighter again after using Feria black means you could melt your hair off if you're not careful.  I'd say consult a pro and make sure you tell him/her you used Feria.  It doesn't work with regular colorstripper, which is what one usually does as part of the process of making dyed black hair lighter.