ΔE 18.1, loose: different enough that you should pick on purpose. Skeleton Brown is a little darker, much more muted, warmer than Brownish Decay.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Skeleton Brown is a little darker, much more muted, warmer than Brownish Decay.
The same difference applies the other way round: Brownish Decay is a little lighter, much more saturated, 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.
See Brownish Decay on the colour wheel See Skeleton Brown on the colour wheel
All matches: Brownish Decay equivalents · Skeleton Brown equivalents