Bastion Grey vs Dark Ghost Gray

How close are they?

ΔE 23.0, loose: different enough that you should pick on purpose. Dark Ghost Gray is noticeably lighter, more muted than Bastion Grey.

Can I use Dark Ghost Gray instead of Bastion Grey?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Dark Ghost Gray is noticeably lighter, more muted than Bastion Grey.

Can I use Bastion Grey instead of Dark Ghost Gray?

The same difference applies the other way round: Bastion Grey is noticeably darker, more saturated.

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.