Nurgling Green vs Bastion Grey

How close are they?

ΔE 20.2, loose: different enough that you should pick on purpose. Bastion Grey is noticeably darker, much more muted, warmer than Nurgling Green.

Can I use Bastion Grey instead of Nurgling Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Bastion Grey is noticeably darker, much more muted, warmer than Nurgling Green.

Can I use Nurgling Green instead of Bastion Grey?

The same difference applies the other way round: Nurgling Green is noticeably lighter, much 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.