Dark Imperial Khaki vs Soft Green

How close are they?

ΔE 15.5, loose: different enough that you should pick on purpose. Soft Green is noticeably lighter, cooler than Dark Imperial Khaki.

Can I use Soft Green instead of Dark Imperial Khaki?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Soft Green is noticeably lighter, cooler than Dark Imperial Khaki.

Can I use Dark Imperial Khaki instead of Soft Green?

The same difference applies the other way round: Dark Imperial Khaki is noticeably darker, 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.