ΔE 11.4, fair: the same colour family, but not a straight swap. Iridescent Pearl (Coarse) is noticeably lighter than Mithril. They are different kinds of paint: Army Painter Mithril is a metallic and Golden Iridescent Pearl (Coarse) is a pearl paint, 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 11). Iridescent Pearl (Coarse) is noticeably lighter than Mithril. They are different kinds of paint.
The same difference applies the other way round: Mithril 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 Mithril on the colour wheel See Iridescent Pearl (Coarse) on the colour wheel
All matches: Mithril equivalents · Iridescent Pearl (Coarse) equivalents