Navy Blue vs Steely Blue

How close are they?

ΔE 6.8, close: similar, with a visible difference side by side. Steely Blue is a little darker, warmer than Navy Blue.

Can I use Steely Blue instead of Navy Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Steely Blue is a little darker, warmer than Navy Blue.

Can I use Navy Blue instead of Steely Blue?

The same difference applies the other way round: Navy Blue is a little lighter, 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.