Thunder Storm vs Dark Sea Blue

How close are they?

ΔE 7.9, close: similar, with a visible difference side by side. Dark Sea Blue is a little lighter than Thunder Storm.

Can I use Dark Sea Blue instead of Thunder Storm?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Dark Sea Blue is a little lighter than Thunder Storm.

Can I use Thunder Storm instead of Dark Sea Blue?

The same difference applies the other way round: Thunder Storm is a little darker.

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.