ΔE 14.3, fair: the same colour family, but not a straight swap. Turquoise is a little darker, warmer than Thunderhawk Blue. They are different kinds of paint: Citadel Thunderhawk Blue is an opaque base/layer paint and Green Stuff World Turquoise is an ink, glaze or transparent 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). Turquoise is a little darker, warmer than Thunderhawk Blue. They are different kinds of paint.
The same difference applies the other way round: Thunderhawk Blue is a little lighter, cooler.
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 Thunderhawk Blue on the colour wheel See Turquoise on the colour wheel
All matches: Thunderhawk Blue equivalents · Turquoise equivalents