Toxic Mist vs Ion Blue

How close are they?

ΔE 7.7, close: similar, with a visible difference side by side. Ion Blue is more muted, cooler than Toxic Mist.

Can I use Ion Blue instead of Toxic Mist?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Ion Blue is more muted, cooler than Toxic Mist.

Can I use Toxic Mist instead of Ion Blue?

The same difference applies the other way round: Toxic Mist 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.