ΔE 10.3, fair: the same colour family, but not a straight swap. Obsidian Black is noticeably darker than Sir Coates Silver.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 10). Obsidian Black is noticeably darker than Sir Coates Silver.
The same difference applies the other way round: Sir Coates Silver 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 Sir Coates Silver on the colour wheel See Obsidian Black on the colour wheel
All matches: Sir Coates Silver equivalents · Obsidian Black equivalents