Ultramarine Blue vs Thunderhawk Blue

How close are they?

ΔE 9.3, close: similar, with a visible difference side by side. Thunderhawk Blue is more muted, cooler than Ultramarine Blue.

Can I use Thunderhawk Blue instead of Ultramarine Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Thunderhawk Blue is more muted, cooler than Ultramarine Blue.

Can I use Ultramarine Blue instead of Thunderhawk Blue?

The same difference applies the other way round: Ultramarine Blue is more saturated, warmer.

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.