ΔE 21.9, loose: different enough that you should pick on purpose. Morrow Purple is a little lighter, much more saturated than Gravelord Grey.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Morrow Purple is a little lighter, much more saturated than Gravelord Grey.
The same difference applies the other way round: Gravelord Grey is a little darker, much more muted.
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 Gravelord Grey on the colour wheel See Morrow Purple on the colour wheel
All matches: Gravelord Grey equivalents · Morrow Purple equivalents