Oak Brown vs Dark Violet

How close are they?

ΔE 15.9, loose: different enough that you should pick on purpose. Dark Violet is a little darker, more saturated, cooler than Oak Brown.

Can I use Dark Violet instead of Oak Brown?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Dark Violet is a little darker, more saturated, cooler than Oak Brown.

Can I use Oak Brown instead of Dark Violet?

The same difference applies the other way round: Oak Brown is a little lighter, more muted, 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.