Nuclear Sunrise vs Gryph-Hound Orange

How close are they?

ΔE 20.4, loose: different enough that you should pick on purpose. Gryph-Hound Orange is a little lighter, more muted than Nuclear Sunrise.

Can I use Gryph-Hound Orange instead of Nuclear Sunrise?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Gryph-Hound Orange is a little lighter, more muted than Nuclear Sunrise.

Can I use Nuclear Sunrise instead of Gryph-Hound Orange?

The same difference applies the other way round: Nuclear Sunrise is a little darker, 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.