ΔE 13.9, fair: the same colour family, but not a straight swap. Frost is noticeably lighter than Skink Blue. They are different kinds of paint: Citadel Skink Blue is an opaque base/layer paint and Vallejo Frost 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). Frost is noticeably lighter than Skink Blue. They are different kinds of paint.
The same difference applies the other way round: Skink Blue is noticeably darker.
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 Skink Blue on the colour wheel See Frost on the colour wheel
All matches: Skink Blue equivalents · Frost equivalents