Bluegrey Dusk vs Midnight Purple

How close are they?

ΔE 8.8, close: similar, with a visible difference side by side. Midnight Purple is a little darker, warmer than Bluegrey Dusk.

Can I use Midnight Purple instead of Bluegrey Dusk?

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

Can I use Bluegrey Dusk instead of Midnight Purple?

The same difference applies the other way round: Bluegrey Dusk 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.