ΔE 18.3, loose: different enough that you should pick on purpose. Flat Yellow is a little darker, much more muted, warmer than Life Vest Yellow.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Flat Yellow is a little darker, much more muted, warmer than Life Vest Yellow.
The same difference applies the other way round: Life Vest Yellow is a little lighter, much more saturated, 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 Life Vest Yellow on the colour wheel See Flat Yellow on the colour wheel
All matches: Life Vest Yellow equivalents · Flat Yellow equivalents