I have a question about coloring a clients hair?

I have a client who is a level 4 black and has been using a box color for years. She now wants to start having me color her hair with professional products. ( I use Shwartskoff) My question is should I try to use a color remover so I can put professional color on her roots and then work it through her ends the last 5 minutes of processing, or should I just color the roots for now to see if the box color fades? I just can't see why I should put a level 4 professional color over her box color. Any suggestions for all the fellow Hair Stylists out there. I would appreciate it.

I have a question about coloring a clients hair?

yeah, sounds good to me

I have a question about coloring a clients hair?

I would suggest that you do the last five minutes on the ends. If you don't you might change the ends a different color if you don't