Aggressor Blue FS 35109 vs Nocturne Green

How close are they?

ΔE 15.9, loose: different enough that you should pick on purpose. Nocturne Green is noticeably darker, cooler than Aggressor Blue FS 35109.

Can I use Nocturne Green instead of Aggressor Blue FS 35109?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Nocturne Green is noticeably darker, cooler than Aggressor Blue FS 35109.

Can I use Aggressor Blue FS 35109 instead of Nocturne Green?

The same difference applies the other way round: Aggressor Blue FS 35109 is noticeably lighter, 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.