ΔE 10.1, fair: the same colour family, but not a straight swap. Fenrisian Grey is a little darker, cooler than Matt Light Lilac Grey. They are different kinds of paint: AMMO by Mig Matt Light Lilac Grey is an ink, glaze or transparent paint and Citadel Fenrisian Grey is an opaque base/layer 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 10). Fenrisian Grey is a little darker, cooler than Matt Light Lilac Grey. They are different kinds of paint.
The same difference applies the other way round: Matt Light Lilac Grey is a little lighter, warmer.
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 Matt Light Lilac Grey on the colour wheel See Fenrisian Grey on the colour wheel
All matches: Matt Light Lilac Grey equivalents · Fenrisian Grey equivalents