Green Uniform Base vs Lupercal Green

How close are they?

ΔE 15.1, loose: different enough that you should pick on purpose. Lupercal Green is a little lighter, cooler than Green Uniform Base.

Can I use Lupercal Green instead of Green Uniform Base?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Lupercal Green is a little lighter, cooler than Green Uniform Base.

Can I use Green Uniform Base instead of Lupercal Green?

The same difference applies the other way round: Green Uniform Base 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.