Summersea Blue vs Andrea Blue

How close are they?

ΔE 9.9, close: similar, with a visible difference side by side. Andrea Blue is more muted, cooler than Summersea Blue.

Can I use Andrea Blue instead of Summersea Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Andrea Blue is more muted, cooler than Summersea Blue.

Can I use Summersea Blue instead of Andrea Blue?

The same difference applies the other way round: Summersea Blue is more saturated, 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.