ΔE 20.7, loose: different enough that you should pick on purpose. Fluorescent Yellow is a little lighter, more saturated, cooler than Yriel Yellow. They are different kinds of paint: Citadel Yriel Yellow is an opaque base/layer paint and Mr. Hobby Fluorescent Yellow is a fluorescent or effect paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Fluorescent Yellow is a little lighter, more saturated, cooler than Yriel Yellow. They are different kinds of paint.
The same difference applies the other way round: Yriel Yellow is a little darker, more muted, 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.
See Yriel Yellow on the colour wheel See Fluorescent Yellow on the colour wheel
All matches: Yriel Yellow equivalents · Fluorescent Yellow equivalents