Castellan Green vs Fern Green

How close are they?

ΔE 9.9, close: similar, with a visible difference side by side. Fern Green is a little lighter, more muted, warmer than Castellan Green.

Can I use Fern Green instead of Castellan Green?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Fern Green is a little lighter, more muted, warmer than Castellan Green.

Can I use Castellan Green instead of Fern Green?

The same difference applies the other way round: Castellan Green is a little darker, more saturated, cooler.

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.