ΔE 11.6, fair: the same colour family, but not a straight swap. Medium Seagray BS381C/637 is more saturated than Regiment Grey.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Medium Seagray BS381C/637 is more saturated than Regiment Grey.
The same difference applies the other way round: Regiment Grey is 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 Medium Seagray BS381C/637 on the colour wheel
All matches: Regiment Grey equivalents · Medium Seagray BS381C/637 equivalents