Gryph-Hound Orange vs Radiant Orange

How close are they?

ΔE 35.9, loose: different enough that you should pick on purpose. Radiant Orange is noticeably darker, much more muted than Gryph-Hound Orange.

Can I use Radiant Orange instead of Gryph-Hound Orange?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 36). Radiant Orange is noticeably darker, much more muted than Gryph-Hound Orange.

Can I use Gryph-Hound Orange instead of Radiant Orange?

The same difference applies the other way round: Gryph-Hound Orange is noticeably lighter, much more saturated.

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.