Dark Blue vs Triumphant Navy

How close are they?

ΔE 7.2, close: similar, with a visible difference side by side. Triumphant Navy is more saturated, warmer than Dark Blue.

Can I use Triumphant Navy instead of Dark Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Triumphant Navy is more saturated, warmer than Dark Blue.

Can I use Dark Blue instead of Triumphant Navy?

The same difference applies the other way round: Dark Blue is more muted, 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.