Pigma
I used to colour my hair at home but now have it done at the salon. My hairdresser told me that mine was very dark when I coloured it myself because of a build up of colour. This would also account for a slight green tinge. She said that any make of colour or the shade of colour would have the same build up. I now have mine coloured every five weeks, at one visit I have an all over colour then for the next two visits I have the roots coloured only and this prevents a build up which apparently would happen with a salon colour as well. On the in between two visits while the roots are ‘doing’ I have a glaze treatment on the lengths to add shine and gloss. The build up of colour when I did it myself meant it never looked shiny.
The downside of course is time and cost.
Might be worth trying at home though by just doing a full colour one time and roots twice in between and maybe a nourishing hair mask on the lengths?
Apologies for not answering your original question but hope this is of some help.
Thank you ... Yes this is what I do mostly, roots only. Just now and again all over.
I can imagine it is a build up, as I colour it so often. Apparently how porous your hair is too.
But as you said the downside being the time and cost.