ΔE 13.9, fair: the same colour family, but not a straight swap. Landser Grey is noticeably lighter than Black Templar.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Landser Grey is noticeably lighter than Black Templar.
The same difference applies the other way round: Black Templar is noticeably 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 Black Templar on the colour wheel See Landser Grey on the colour wheel
All matches: Black Templar equivalents · Landser Grey equivalents