ΔE 13.7, fair: the same colour family, but not a straight swap. Fluorescent Orange is much more saturated than Trollslayer Orange. They are different kinds of paint: Citadel Trollslayer Orange is an opaque base/layer paint and Pro Acryl Fluorescent Orange is a fluorescent or effect 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 14). Fluorescent Orange is much more saturated than Trollslayer Orange. They are different kinds of paint.
The same difference applies the other way round: Trollslayer Orange is much 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 Trollslayer Orange on the colour wheel See Fluorescent Orange on the colour wheel
All matches: Trollslayer Orange equivalents · Fluorescent Orange equivalents