Fluorescent Yellow vs Bile

How close are they?

ΔE 40.3, loose: different enough that you should pick on purpose. Bile is noticeably darker, more muted, cooler than Fluorescent Yellow.

Can I use Bile instead of Fluorescent Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 40). Bile is noticeably darker, more muted, cooler than Fluorescent Yellow.

Can I use Fluorescent Yellow instead of Bile?

The same difference applies the other way round: Fluorescent Yellow is noticeably lighter, more saturated, warmer.

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.