ΔE 12.6, fair: the same colour family, but not a straight swap. Obsidian Black is a little lighter than Rainbow Roll.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Obsidian Black is a little lighter than Rainbow Roll.
The same difference applies the other way round: Rainbow Roll is a little darker.
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 Rainbow Roll on the colour wheel See Obsidian Black on the colour wheel
All matches: Rainbow Roll equivalents · Obsidian Black equivalents