Dark Elf Highlight vs Russian AF Grey N.3

How close are they?

ΔE 8.5, close: similar, with a visible difference side by side. Russian AF Grey N.3 is a little lighter than Dark Elf Highlight.

Can I use Russian AF Grey N.3 instead of Dark Elf Highlight?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Russian AF Grey N.3 is a little lighter than Dark Elf Highlight.

Can I use Dark Elf Highlight instead of Russian AF Grey N.3?

The same difference applies the other way round: Dark Elf Highlight is a little darker.

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.