Thunder Storm vs Bluegrey Dusk

How close are they?

ΔE 8.8, close: similar, with a visible difference side by side. Bluegrey Dusk is a little lighter, warmer than Thunder Storm.

Can I use Bluegrey Dusk instead of Thunder Storm?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Bluegrey Dusk is a little lighter, warmer than Thunder Storm.

Can I use Thunder Storm instead of Bluegrey Dusk?

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