ΔE 30.6, loose: different enough that you should pick on purpose. Blueberry is noticeably darker, much more saturated than Ignis Fatuus.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 31). Blueberry is noticeably darker, much more saturated than Ignis Fatuus.
The same difference applies the other way round: Ignis Fatuus is noticeably 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 Ignis Fatuus on the colour wheel See Blueberry on the colour wheel
All matches: Ignis Fatuus equivalents · Blueberry equivalents