Russian Dark Brown 6K vs Rhinox Hide

How close are they?

ΔE 15.4, loose: different enough that you should pick on purpose. Rhinox Hide is a little lighter, warmer than Russian Dark Brown 6K.

Can I use Rhinox Hide instead of Russian Dark Brown 6K?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Rhinox Hide is a little lighter, warmer than Russian Dark Brown 6K.

Can I use Russian Dark Brown 6K instead of Rhinox Hide?

The same difference applies the other way round: Russian Dark Brown 6K is a little darker, cooler.

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.