Undergrowth Green vs Sick Green

How close are they?

ΔE 7.2, close: similar, with a visible difference side by side. Sick Green is a little lighter, more saturated than Undergrowth Green.

Can I use Sick Green instead of Undergrowth Green?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Sick Green is a little lighter, more saturated than Undergrowth Green.

Can I use Undergrowth Green instead of Sick Green?

The same difference applies the other way round: Undergrowth Green is a little darker, more muted.

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.