ΔE 12.3, fair: the same colour family, but not a straight swap. Transparent Sepia is noticeably darker, more muted than Balor Brown. They are different kinds of paint: Citadel Balor Brown is an opaque base/layer paint and Green Stuff World Transparent Sepia 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 12). Transparent Sepia is noticeably darker, more muted than Balor Brown. They are different kinds of paint.
The same difference applies the other way round: Balor Brown is noticeably lighter, more saturated.
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 Balor Brown on the colour wheel See Transparent Sepia on the colour wheel
All matches: Balor Brown equivalents · Transparent Sepia equivalents