ΔE 11.0, fair: the same colour family, but not a straight swap. Cement Grey is a little lighter, more muted, warmer than Flat Green.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Cement Grey is a little lighter, more muted, warmer than Flat Green.
The same difference applies the other way round: Flat Green is a little darker, more saturated, cooler.
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 Flat Green on the colour wheel See Cement Grey on the colour wheel
All matches: Flat Green equivalents · Cement Grey equivalents