ΔE 11.4, fair: the same colour family, but not a straight swap. Troll Shadow is a little darker, more muted, cooler than Sepia Tone. They are different kinds of paint: Army Painter Sepia Tone is a wash/shade and Reaper Troll Shadow is an opaque base/layer paint, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Troll Shadow is a little darker, more muted, cooler than Sepia Tone. They are different kinds of paint.
The same difference applies the other way round: Sepia Tone 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 Sepia Tone on the colour wheel See Troll Shadow on the colour wheel
All matches: Sepia Tone equivalents · Troll Shadow equivalents