ΔE 6.3, close: similar, with a visible difference side by side. Phthalo Green (Blue Shade) is a little lighter than Medieval Forest. They are different kinds of paint: Army Painter Medieval Forest is an opaque base/layer paint and Golden Phthalo Green (Blue Shade) 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 6). Phthalo Green (Blue Shade) is a little lighter than Medieval Forest. They are different kinds of paint.
The same difference applies the other way round: Medieval Forest 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 Medieval Forest on the colour wheel See Phthalo Green (Blue Shade) on the colour wheel
All matches: Medieval Forest equivalents · Phthalo Green (Blue Shade) equivalents