Teclis Blue vs Summersea Blue

How close are they?

ΔE 6.5, close: similar, with a visible difference side by side. Summersea Blue is a little darker than Teclis Blue.

Can I use Summersea Blue instead of Teclis Blue?

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

Can I use Teclis Blue instead of Summersea Blue?

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

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.