Shadow Orange vs Viper Brown

How close are they?

ΔE 8.2, close: similar, with a visible difference side by side. Viper Brown is a little darker, more muted than Shadow Orange.

Can I use Viper Brown instead of Shadow Orange?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Viper Brown is a little darker, more muted than Shadow Orange.

Can I use Shadow Orange instead of Viper Brown?

The same difference applies the other way round: Shadow Orange is a little lighter, 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.