Toxic Mist vs Frostbite

How close are they?

ΔE 21.1, loose: different enough that you should pick on purpose. Frostbite is noticeably lighter, much more muted than Toxic Mist.

Can I use Frostbite instead of Toxic Mist?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Frostbite is noticeably lighter, much more muted than Toxic Mist.

Can I use Toxic Mist instead of Frostbite?

The same difference applies the other way round: Toxic Mist is noticeably darker, much more saturated.

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.