ΔE 10.5, fair: the same colour family, but not a straight swap. Crusader Skin is a little lighter, more saturated than Matt Sepia. They are different kinds of paint: AMMO by Mig Matt Sepia is an ink, glaze or transparent paint and Army Painter Crusader Skin is a one-coat contrast-style 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 11). Crusader Skin is a little lighter, more saturated than Matt Sepia. They are different kinds of paint.
The same difference applies the other way round: Matt Sepia is a little darker, more muted.
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 Matt Sepia on the colour wheel See Crusader Skin on the colour wheel
All matches: Matt Sepia equivalents · Crusader Skin equivalents