Castellan Green vs Flat Green

How close are they?

ΔE 9.1, close: similar, with a visible difference side by side. Flat Green is more muted, warmer than Castellan Green.

Can I use Flat Green instead of Castellan Green?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Flat Green is more muted, warmer than Castellan Green.

Can I use Castellan Green instead of Flat Green?

The same difference applies the other way round: Castellan Green is 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.