Pastel Yellow vs Acid Green

How close are they?

ΔE 20.6, loose: different enough that you should pick on purpose. Acid Green is a little darker, more muted, cooler than Pastel Yellow.

Can I use Acid Green instead of Pastel Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Acid Green is a little darker, more muted, cooler than Pastel Yellow.

Can I use Pastel Yellow instead of Acid Green?

The same difference applies the other way round: Pastel Yellow is a little 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.