ΔE 22.3, loose: different enough that you should pick on purpose. Sepia Wash is a little darker, much more saturated than Soulblight Grey.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Sepia Wash is a little darker, much more saturated than Soulblight Grey.
The same difference applies the other way round: Soulblight Grey is a little lighter, much 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 Soulblight Grey on the colour wheel See Sepia Wash on the colour wheel
All matches: Soulblight Grey equivalents · Sepia Wash equivalents