ΔE 12.6, fair: the same colour family, but not a straight swap. Medium Sea Grey is noticeably darker than N6 Neutral Gray.
Can I use Medium Sea Grey instead of N6 Neutral Gray?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Medium Sea Grey is noticeably darker than N6 Neutral Gray.
Can I use N6 Neutral Gray instead of Medium Sea Grey?
The same difference applies the other way round: N6 Neutral Gray 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.