ΔE 15.7, loose: different enough that you should pick on purpose. Chestnut Brown is a little darker, more muted, cooler than Reikland Fleshshade. They are different kinds of paint: Citadel Reikland Fleshshade is a wash/shade and Nocturna Models Chestnut Brown is an opaque base/layer paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Chestnut Brown is a little darker, more muted, cooler than Reikland Fleshshade. They are different kinds of paint.
The same difference applies the other way round: Reikland Fleshshade is a little lighter, more saturated, 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 Reikland Fleshshade on the colour wheel See Chestnut Brown on the colour wheel
All matches: Reikland Fleshshade equivalents · Chestnut Brown equivalents