ΔE 11.3, fair: the same colour family, but not a straight swap. Iridescent Purple/Green is more saturated than Stormhost Silver. They are different kinds of paint: Citadel Stormhost Silver is a metallic and Tamiya Iridescent Purple/Green 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 Purple/Green is more saturated than Stormhost Silver. They are different kinds of paint.
The same difference applies the other way round: Stormhost Silver is more muted.
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 Stormhost Silver on the colour wheel See Iridescent Purple/Green on the colour wheel
All matches: Stormhost Silver equivalents · Iridescent Purple/Green equivalents