ΔE 13.7, fair: the same colour family, but not a straight swap. Dark Reaper is noticeably darker, cooler than Green Grey.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Dark Reaper is noticeably darker, cooler than Green Grey.
The same difference applies the other way round: Green Grey is noticeably lighter, warmer.
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 Green Grey on the colour wheel See Dark Reaper on the colour wheel
All matches: Green Grey equivalents · Dark Reaper equivalents