ΔE 10.3, fair: the same colour family, but not a straight swap. Trollslayer Orange is a little lighter, more saturated than Light Rust. They are different kinds of paint: AMMO by Mig Light Rust is an ink, glaze or transparent paint and Citadel Trollslayer Orange is an opaque base/layer 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 10). Trollslayer Orange is a little lighter, more saturated than Light Rust. They are different kinds of paint.
The same difference applies the other way round: Light Rust is a little darker, 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 Light Rust on the colour wheel See Trollslayer Orange on the colour wheel
All matches: Light Rust equivalents · Trollslayer Orange equivalents