ΔE 26.9, loose: different enough that you should pick on purpose. Imperial Yellow is a little darker, warmer than Warm Yellow.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 27). Imperial Yellow is a little darker, warmer than Warm Yellow.
The same difference applies the other way round: Warm Yellow 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 Warm Yellow on the colour wheel See Imperial Yellow on the colour wheel
All matches: Warm Yellow equivalents · Imperial Yellow equivalents