Orc Green vs Sick Green

How close are they?

ΔE 15.8, loose: different enough that you should pick on purpose. Sick Green is a little lighter, much more saturated, warmer than Orc Green.

Can I use Sick Green instead of Orc Green?

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

Can I use Orc Green instead of Sick Green?

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