ΔE 14.9, fair: the same colour family, but not a straight swap. A-28M Greyish Blue is noticeably lighter, more muted, warmer than Phthalo Green.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 15). A-28M Greyish Blue is noticeably lighter, more muted, warmer than Phthalo Green.
The same difference applies the other way round: Phthalo Green is noticeably 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 Phthalo Green on the colour wheel See A-28M Greyish Blue on the colour wheel
All matches: Phthalo Green equivalents · A-28M Greyish Blue equivalents