Viridian Green vs Foul Green

How close are they?

ΔE 14.3, fair: the same colour family, but not a straight swap. Foul Green is noticeably lighter than Viridian Green.

Can I use Foul Green instead of Viridian Green?

Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Foul Green is noticeably lighter than Viridian Green.

Can I use Viridian Green instead of Foul Green?

The same difference applies the other way round: Viridian Green 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.