ΔE 8.6, close: similar, with a visible difference side by side. Viridis Green is a little lighter than Majestic Fortress. They are different kinds of paint: Army Painter Majestic Fortress is an opaque base/layer paint and Green Stuff World Viridis Green 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 9). Viridis Green is a little lighter than Majestic Fortress. They are different kinds of paint.
The same difference applies the other way round: Majestic Fortress is a little darker.
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 Majestic Fortress on the colour wheel See Viridis Green on the colour wheel
All matches: Majestic Fortress equivalents · Viridis Green equivalents