Space Green vs Olive Green

How close are they?

ΔE 16.3, loose: different enough that you should pick on purpose. Olive Green is a little darker, much more muted, warmer than Space Green.

Can I use Olive Green instead of Space Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Olive Green is a little darker, much more muted, warmer than Space Green.

Can I use Space Green instead of Olive Green?

The same difference applies the other way round: Space Green is a little lighter, much 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.