Aquamarine vs Soft Green

How close are they?

ΔE 20.7, loose: different enough that you should pick on purpose. Soft Green is a little darker, more muted, warmer than Aquamarine.

Can I use Soft Green instead of Aquamarine?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Soft Green is a little darker, more muted, warmer than Aquamarine.

Can I use Aquamarine instead of Soft Green?

The same difference applies the other way round: Aquamarine is a little lighter, 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.