ΔE 11.6, fair: the same colour family, but not a straight swap. Hearthborn is more saturated, warmer than Portland Stone No.64.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Hearthborn is more saturated, warmer than Portland Stone No.64.
The same difference applies the other way round: Portland Stone No.64 is more muted, 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 Portland Stone No.64 on the colour wheel See Hearthborn on the colour wheel
All matches: Portland Stone No.64 equivalents · Hearthborn equivalents