Yellow Green vs Dark Yellow

How close are they?

ΔE 15.7, loose: different enough that you should pick on purpose. Dark Yellow is much more muted, warmer than Yellow Green.

Can I use Dark Yellow instead of Yellow Green?

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

Can I use Yellow Green instead of Dark Yellow?

The same difference applies the other way round: Yellow Green is 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.