Greatcoat Green vs Dark Yellow Green

How close are they?

ΔE 17.9, loose: different enough that you should pick on purpose. Dark Yellow Green is noticeably darker, more muted, cooler than Greatcoat Green.

Can I use Dark Yellow Green instead of Greatcoat Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Dark Yellow Green is noticeably darker, more muted, cooler than Greatcoat Green.

Can I use Greatcoat Green instead of Dark Yellow Green?

The same difference applies the other way round: Greatcoat Green is noticeably lighter, more saturated, 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.