Russ Grey vs Dark Concrete

How close are they?

ΔE 20.8, loose: different enough that you should pick on purpose. Dark Concrete is noticeably darker, much more muted than Russ Grey.

Can I use Dark Concrete instead of Russ Grey?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Dark Concrete is noticeably darker, much more muted than Russ Grey.

Can I use Russ Grey instead of Dark Concrete?

The same difference applies the other way round: Russ Grey is noticeably lighter, much 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.