Irati Green vs Sick Green

How close are they?

ΔE 15.5, loose: different enough that you should pick on purpose. Sick Green is a little lighter, more saturated, warmer than Irati Green.

Can I use Sick Green instead of Irati Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Sick Green is a little lighter, more saturated, warmer than Irati Green.

Can I use Irati Green instead of Sick Green?

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