Dwarf Shield vs Radiant Yellow

How close are they?

ΔE 24.3, loose: different enough that you should pick on purpose. Radiant Yellow is noticeably lighter, more saturated, cooler than Dwarf Shield.

Can I use Radiant Yellow instead of Dwarf Shield?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Radiant Yellow is noticeably lighter, more saturated, cooler than Dwarf Shield.

Can I use Dwarf Shield instead of Radiant Yellow?

The same difference applies the other way round: Dwarf Shield is noticeably 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.