Stormfang vs Phthalo Turquoise Light

How close are they?

ΔE 9.0, close: similar, with a visible difference side by side. Phthalo Turquoise Light is more saturated than Stormfang.

Can I use Phthalo Turquoise Light instead of Stormfang?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Phthalo Turquoise Light is more saturated than Stormfang.

Can I use Stormfang instead of Phthalo Turquoise Light?

The same difference applies the other way round: Stormfang is more muted.

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.