ΔE 14.3, fair: the same colour family, but not a straight swap. Red Glaze is noticeably lighter, cooler than Fyreslayer Flesh. They are different kinds of paint: Citadel Fyreslayer Flesh is a one-coat contrast-style paint and Two Thin Coats Red Glaze 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). Red Glaze is noticeably lighter, cooler than Fyreslayer Flesh. They are different kinds of paint.
The same difference applies the other way round: Fyreslayer Flesh is noticeably darker, warmer.
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 Fyreslayer Flesh on the colour wheel See Red Glaze on the colour wheel
All matches: Fyreslayer Flesh equivalents · Red Glaze equivalents