Grim Rust vs Techno Green

How close are they?

ΔE 81.0, loose: different enough that you should pick on purpose. Techno Green is a little lighter, more saturated, cooler than Grim Rust.

Can I use Techno Green instead of Grim Rust?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 81). Techno Green is a little lighter, more saturated, cooler than Grim Rust.

Can I use Grim Rust instead of Techno Green?

The same difference applies the other way round: Grim Rust is a little darker, more muted, warmer.

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.