ΔE 10.9, fair: the same colour family, but not a straight swap. Phthalo Green (Blue Shade) is a little lighter, more muted, warmer than Akhelian Green. They are different kinds of paint: Citadel Akhelian Green is a one-coat contrast-style 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.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Phthalo Green (Blue Shade) is a little lighter, more muted, warmer than Akhelian Green. They are different kinds of paint.
The same difference applies the other way round: Akhelian Green is a little darker, more saturated, cooler.
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 Akhelian Green on the colour wheel See Phthalo Green (Blue Shade) on the colour wheel
All matches: Akhelian Green equivalents · Phthalo Green (Blue Shade) equivalents