ΔE 13.4, fair: the same colour family, but not a straight swap. Obsidian Black is noticeably lighter than Iridescent Stainless Steel (Coarse). They are different kinds of paint: Golden Iridescent Stainless Steel (Coarse) is a pearl paint and Vallejo Obsidian Black is a metallic, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Obsidian Black is noticeably lighter than Iridescent Stainless Steel (Coarse). They are different kinds of paint.
The same difference applies the other way round: Iridescent Stainless Steel (Coarse) is noticeably 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 Iridescent Stainless Steel (Coarse) on the colour wheel See Obsidian Black on the colour wheel
All matches: Iridescent Stainless Steel (Coarse) equivalents · Obsidian Black equivalents