Gun Metal vs Toxic Purple

How close are they?

ΔE 43.3, loose: different enough that you should pick on purpose. Toxic Purple is a little lighter, much more saturated than Gun Metal.

Can I use Toxic Purple instead of Gun Metal?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 43). Toxic Purple is a little lighter, much more saturated than Gun Metal.

Can I use Gun Metal instead of Toxic Purple?

The same difference applies the other way round: Gun Metal is a little darker, much 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.