Hair colour help

[Vinnie1965]

My clients natural hair colour is a base6. I used koleston perfect 6/0 & 20vol to cover a very few grey hairs. The roots lifted to a base 8/0 - why would that be & what would you suggest to use next time? Many thanks in advance

 

[AcidPerm]

Few grey hairs? what percentage are we talking?
Of course it’s going to lift natural hair with 20vol but the tint should have covered it.