Gryph-Hound Orange vs Nuclear Yellow

How close are they?

ΔE 6.7, close: similar, with a visible difference side by side. Nuclear Yellow is a little darker than Gryph-Hound Orange.

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

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Nuclear Yellow is a little darker than Gryph-Hound Orange.

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

The same difference applies the other way round: Gryph-Hound Orange is a little lighter.

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.