ΔE 21.3, loose: different enough that you should pick on purpose. Skeleton Horde is a little darker, much more muted, warmer than Matt Light Yellow. They are different kinds of paint: AMMO by Mig Matt Light Yellow is an ink, glaze or transparent paint and Citadel Skeleton Horde is a one-coat contrast-style 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). Skeleton Horde is a little darker, much more muted, warmer than Matt Light Yellow. They are different kinds of paint.
The same difference applies the other way round: Matt Light 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 Matt Light Yellow on the colour wheel See Skeleton Horde on the colour wheel
All matches: Matt Light Yellow equivalents · Skeleton Horde equivalents