Gray Resistant to Permanent Hair Dye

I have graying hair that is somewhat resistant to color. I use permanent hair color one of the NN products or Paul Mitchell 6+ to cover the gray. However it does not last. I have tried now, to use Paul Mitchell pm shines, RV and added 3 V to get the depth I want. I like the color but it is a bit too dark. Also, I will notice a line where new regrowth has started. I have tried 6Vr and it seems to hold better than the RV.

Basically, I am coloring my hair with permanent hair color, roots only, and then coloring with pm shines. I would like to get the color with of the pm shines with permanent hair color. Do you have any suggestions