Aqua Alchemy vs Tropical Turquoise

How close are they?

ΔE 6.3, close: similar, with a visible difference side by side. Tropical Turquoise is cooler than Aqua Alchemy.

Can I use Tropical Turquoise instead of Aqua Alchemy?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). Tropical Turquoise is cooler than Aqua Alchemy.

Can I use Aqua Alchemy instead of Tropical Turquoise?

The same difference applies the other way round: Aqua Alchemy is 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.