Protective Green 1920s-1930s vs Lupercal Green

How close are they?

ΔE 12.3, fair: the same colour family, but not a straight swap. Lupercal Green is a little lighter, cooler than Protective Green 1920s-1930s.

Can I use Lupercal Green instead of Protective Green 1920s-1930s?

Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Lupercal Green is a little lighter, cooler than Protective Green 1920s-1930s.

Can I use Protective Green 1920s-1930s instead of Lupercal Green?

The same difference applies the other way round: Protective Green 1920s-1930s is a little darker, 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.