Thunderhawk Blue vs Caspian Blue

How close are they?

ΔE 9.9, close: similar, with a visible difference side by side. Caspian Blue is a little lighter, cooler than Thunderhawk Blue.

Can I use Caspian Blue instead of Thunderhawk Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Caspian Blue is a little lighter, cooler than Thunderhawk Blue.

Can I use Thunderhawk Blue instead of Caspian Blue?

The same difference applies the other way round: Thunderhawk Blue is a little darker, 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.