Iron Wolf vs Light Gray

How close are they?

ΔE 6.8, close: similar, with a visible difference side by side. Light Gray is a little lighter, cooler than Iron Wolf.

Can I use Light Gray instead of Iron Wolf?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Light Gray is a little lighter, cooler than Iron Wolf.

Can I use Iron Wolf instead of Light Gray?

The same difference applies the other way round: Iron Wolf is a little darker, 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.