Northern Flesh vs Wolf Grey

How close are they?

ΔE 15.9, loose: different enough that you should pick on purpose. Wolf Grey is a little darker, more muted than Northern Flesh.

Can I use Wolf Grey instead of Northern Flesh?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Wolf Grey is a little darker, more muted than Northern Flesh.

Can I use Northern Flesh instead of Wolf Grey?

The same difference applies the other way round: Northern Flesh is a little lighter, 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.