ΔE 14.1, fair: the same colour family, but not a straight swap. Stonewall Grey is noticeably darker than Leather White.
Can I use Stonewall Grey instead of Leather White?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Stonewall Grey is noticeably darker than Leather White.
Can I use Leather White instead of Stonewall Grey?
The same difference applies the other way round: Leather White 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.