RLM 83 vs Thunderhawk Blue

How close are they?

ΔE 6.9, close: similar, with a visible difference side by side. Thunderhawk Blue is more saturated, cooler than RLM 83.

Can I use Thunderhawk Blue instead of RLM 83?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Thunderhawk Blue is more saturated, cooler than RLM 83.

Can I use RLM 83 instead of Thunderhawk Blue?

The same difference applies the other way round: RLM 83 is more muted, 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.