Straken Green vs Merm Green

How close are they?

ΔE 16.3, loose: different enough that you should pick on purpose. Merm Green is a little darker, much more muted than Straken Green.

Can I use Merm Green instead of Straken Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Merm Green is a little darker, much more muted than Straken Green.

Can I use Straken Green instead of Merm Green?

The same difference applies the other way round: Straken Green is a little 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.