Using colorfix and recoloring dark hair

 

Here's my hair background: naturally dark brown hair w/grays. Right now

I have a dark brown semipermanent (natural instints) OVER a permanent medium reddish brown. The semi has washed out a lot in the back but it is still pretty dark in the front...

 

I'm using the colorfix to remove the dark semi before applying my color-Loreal excellence creme in light ash brown.

 

I know my roots will probably turn a little brassy since my hair is dark, but my question is should i color my roots first, or the lengths to make sure everything comes out even?  Does it even matter since im using color fix?

TIA!!