Sun Stone vs Yriel Yellow

How close are they?

ΔE 15.3, loose: different enough that you should pick on purpose. Yriel Yellow is a little lighter, cooler than Sun Stone.

Can I use Yriel Yellow instead of Sun Stone?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Yriel Yellow is a little lighter, cooler than Sun Stone.

Can I use Sun Stone instead of Yriel Yellow?

The same difference applies the other way round: Sun Stone is a little darker, 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.