ΔE 12.7, fair: the same colour family, but not a straight swap. Transparent Magenta is more muted, cooler than Evil Sunz Scarlet. They are different kinds of paint: Citadel Evil Sunz Scarlet is an opaque base/layer paint and Green Stuff World Transparent Magenta 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 13). Transparent Magenta is more muted, cooler than Evil Sunz Scarlet. They are different kinds of paint.
The same difference applies the other way round: Evil Sunz Scarlet is more saturated, 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 Evil Sunz Scarlet on the colour wheel See Transparent Magenta on the colour wheel
All matches: Evil Sunz Scarlet equivalents · Transparent Magenta equivalents