ΔE 11.3, fair: the same colour family, but not a straight swap. is a little lighter than Grey Knights Steel.
Can I use instead of Grey Knights Steel?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). is a little lighter than Grey Knights Steel.
Can I use Grey Knights Steel instead of ?
The same difference applies the other way round: Grey Knights Steel 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.