The Wn would be culprut of the copper outcome. For levels 7,8,9, for tintback
,its best to stick with the missing gold pigments especially when applying a N shade for target color. The N shade has the perfect balance of red,yellow,red,pigments needed for that levels true balance. The gold mousse if just pure gold no darker than a lv.8, would be good for filling the porous hair from prior bleaching and wouldnt over grabb any unwanted color just gold. Just a lv.8N would be needed on completly dried hair applied about 10 mins after mixing up to avoid the lifting stage and go straight on to the depositing stage.
When you look at a target color in this case a 8N, you would detect no warmth to it but a neutral cooler tone or what I call balanced ash. As color it has the correct amount of red needed from the RGB makeup.I typically don't bother with any warmth not gold/yellow untill a lv.5 or darker.. I havr found that a 50/50 mix of say 6G+6N is adequate for tintbacks/lo-liting without prepig unless hair is more porous needing the extra gold to fill it in for the base to stick better/last longer.