ΔE 11.0, fair: the same colour family, but not a straight swap. Quartz Magenta is a little lighter than Doomfire Magenta. They are different kinds of paint: Citadel Doomfire Magenta is a one-coat contrast-style paint and Green Stuff World Quartz Magenta is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Quartz Magenta is a little lighter than Doomfire Magenta. They are different kinds of paint.
The same difference applies the other way round: Doomfire Magenta is a little darker.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Doomfire Magenta on the colour wheel See Quartz Magenta on the colour wheel
All matches: Doomfire Magenta equivalents · Quartz Magenta equivalents