ΔE 27.3, loose: different enough that you should pick on purpose. Ignis Fatuus is a little lighter, warmer than Baharroth Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 27). Ignis Fatuus is a little lighter, warmer than Baharroth Blue.
The same difference applies the other way round: Baharroth Blue is a little darker, 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 Baharroth Blue on the colour wheel See Ignis Fatuus on the colour wheel
All matches: Baharroth Blue equivalents · Ignis Fatuus equivalents