ΔE 10.5, fair: the same colour family, but not a straight swap. Terror Blue-Grey is a little darker, more saturated than Regiment Grey.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Terror Blue-Grey is a little darker, more saturated than Regiment Grey.
The same difference applies the other way round: Regiment Grey is a little lighter, more muted.
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 Regiment Grey on the colour wheel See Terror Blue-Grey on the colour wheel
All matches: Regiment Grey equivalents · Terror Blue-Grey equivalents