ΔE 6.7, close: similar, with a visible difference side by side. Fire Red is cooler than Martian Ironcrust. They are different kinds of paint: Citadel Martian Ironcrust is a technical paint or medium and Vallejo Fire Red is an opaque base/layer paint, so they won’t behave the same on the model even where the colour is close.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Fire Red is cooler than Martian Ironcrust. They are different kinds of paint.
The same difference applies the other way round: Martian Ironcrust is warmer.
ΔE is the colour difference between our two swatch estimates: under 2 is a perfect match (you’d struggle to tell them apart), under 6 very close, under 10 close, under 15 fair, under 20 loose, under 30 very loose, and 30 or more a poor match. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Martian Ironcrust on the colour wheel See Fire Red on the colour wheel
All matches: Martian Ironcrust equivalents · Fire Red equivalents