Dark Concrete vs Light Green RLM25

How close are they?

ΔE 21.0, loose: different enough that you should pick on purpose. Light Green RLM25 is a little lighter, much more saturated than Dark Concrete.

Can I use Light Green RLM25 instead of Dark Concrete?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Light Green RLM25 is a little lighter, much more saturated than Dark Concrete.

Can I use Dark Concrete instead of Light Green RLM25?

The same difference applies the other way round: Dark Concrete is a little darker, 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.