ΔE 15.0, loose: different enough that you should pick on purpose. Indigo is a little darker, warmer than The Fang.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Indigo is a little darker, warmer than The Fang.
The same difference applies the other way round: The Fang is a little lighter, cooler.
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 The Fang on the colour wheel See Indigo on the colour wheel
All matches: The Fang equivalents · Indigo equivalents