ΔE 10.5, fair: the same colour family, but not a straight swap. Space Wolves Grey is a little lighter than Blue Gray. They are different kinds of paint: AMMO by Mig Blue Gray is an opaque base/layer paint and Citadel Space Wolves Grey is a one-coat contrast-style 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). Space Wolves Grey is a little lighter than Blue Gray. They are different kinds of paint.
The same difference applies the other way round: Blue Gray 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 Blue Gray on the colour wheel See Space Wolves Grey on the colour wheel
All matches: Blue Gray equivalents · Space Wolves Grey equivalents