ΔE 10.5, fair: the same colour family, but not a straight swap. Regiment Grey is a little darker than Dark Sea Grey.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 10). Regiment Grey is a little darker than Dark Sea Grey.
The same difference applies the other way round: Dark Sea Grey is a little lighter.
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 Dark Sea Grey on the colour wheel See Regiment Grey on the colour wheel
All matches: Dark Sea Grey equivalents · Regiment Grey equivalents