ΔE 17.3, loose: different enough that you should pick on purpose. Ruby Red is much more saturated, cooler than Reikland Fleshshade. They are different kinds of paint: Citadel Reikland Fleshshade is a wash/shade and Nocturna Models Ruby Red 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 17). Ruby Red is much more saturated, cooler than Reikland Fleshshade. They are different kinds of paint.
The same difference applies the other way round: Reikland Fleshshade is much 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.
See Reikland Fleshshade on the colour wheel See Ruby Red on the colour wheel
All matches: Reikland Fleshshade equivalents · Ruby Red equivalents