ΔE 40.1, loose: different enough that you should pick on purpose. Flesh Wash is noticeably lighter, cooler than Petroleum Brown Wash.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 40). Flesh Wash is noticeably lighter, cooler than Petroleum Brown Wash.
The same difference applies the other way round: Petroleum Brown Wash is noticeably 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.
See Petroleum Brown Wash on the colour wheel See Flesh Wash on the colour wheel
All matches: Petroleum Brown Wash equivalents · Flesh Wash equivalents