ΔE 11.5, fair: the same colour family, but not a straight swap. Bright Slate Grey is noticeably darker than Ashen Stone.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Bright Slate Grey is noticeably darker than Ashen Stone.
The same difference applies the other way round: Ashen Stone is noticeably lighter.
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 Ashen Stone on the colour wheel See Bright Slate Grey on the colour wheel
All matches: Ashen Stone equivalents · Bright Slate Grey equivalents