RAF Dark Earth vs Cypress Brown

How close are they?

ΔE 7.9, close: similar, with a visible difference side by side. Cypress Brown is a little darker than RAF Dark Earth.

Can I use Cypress Brown instead of RAF Dark Earth?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Cypress Brown is a little darker than RAF Dark Earth.

Can I use RAF Dark Earth instead of Cypress Brown?

The same difference applies the other way round: RAF Dark Earth is a little lighter.

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.