Thallax Gold vs Radiant Yellow

How close are they?

ΔE 22.2, loose: different enough that you should pick on purpose. Radiant Yellow is noticeably lighter, cooler than Thallax Gold.

Can I use Radiant Yellow instead of Thallax Gold?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Radiant Yellow is noticeably lighter, cooler than Thallax Gold.

Can I use Thallax Gold instead of Radiant Yellow?

The same difference applies the other way round: Thallax Gold is noticeably 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.