Turquoise Siren vs Seraphon Blue

How close are they?

ΔE 9.8, close: similar, with a visible difference side by side. Seraphon Blue is more saturated, warmer than Turquoise Siren.

Can I use Seraphon Blue instead of Turquoise Siren?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Seraphon Blue is more saturated, warmer than Turquoise Siren.

Can I use Turquoise Siren instead of Seraphon Blue?

The same difference applies the other way round: Turquoise Siren is more muted, 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.