Hi! I just did a corrective color on my sister because she had some green undertones going on. I did a copper red permanent w/ a 10 developer (to make it a demi). It's looks pretty good but being the perfectionist that I am I noticed that the regrowth was a little brighter. What should I have done to prevent that?. or what should I do for next time to correct it?

Since the dye will react differently with the uncolored regrowth and the greenish ends, you have to treat it differentially -- or don't touch the roots at all.

Actually, it's likely that the roots will fade while the ends probably won't. By the way, simply using 10-volume developer doesn't make permanent color into a demi-permanent. It will make it deposit more pigment and it will also limit the bleaching of the undertones. It's also possible that the color will fade faster than if you had used 20-volume. Nevertheless, the color will penetrate more than a demi-permanent color would have, and thus it will be more permanent.