ΔE 12.4, fair: the same colour family, but not a straight swap. Shadowed Green is noticeably lighter, more saturated than Green Tone. They are different kinds of paint: Army Painter Green Tone is a wash/shade and Reaper Shadowed Green 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 12). Shadowed Green is noticeably lighter, more saturated than Green Tone. They are different kinds of paint.
The same difference applies the other way round: Green Tone is noticeably darker, 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 Green Tone on the colour wheel See Shadowed Green on the colour wheel
All matches: Green Tone equivalents · Shadowed Green equivalents