ΔE 7.1, close: similar, with a visible difference side by side. Siena is a little darker, more saturated than Reikland Fleshshade. They are different kinds of paint: Citadel Reikland Fleshshade is a wash/shade and Green Stuff World Siena is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Siena is a little darker, more saturated than Reikland Fleshshade. They are different kinds of paint.
The same difference applies the other way round: Reikland Fleshshade is a little lighter, more muted.
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 Siena on the colour wheel
All matches: Reikland Fleshshade equivalents · Siena equivalents