N8 Neutral Gray vs Ink Green

How close are they?

ΔE 62.8, loose: different enough that you should pick on purpose. Ink Green is noticeably darker, much more saturated than N8 Neutral Gray.

Can I use Ink Green instead of N8 Neutral Gray?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 63). Ink Green is noticeably darker, much more saturated than N8 Neutral Gray.

Can I use N8 Neutral Gray instead of Ink Green?

The same difference applies the other way round: N8 Neutral Gray is noticeably lighter, much more muted.

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.