ΔE 11.8, fair: the same colour family, but not a straight swap. Rust Orange is a little darker, more saturated, cooler than Viper Brown.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Rust Orange is a little darker, more saturated, cooler than Viper Brown.
The same difference applies the other way round: Viper Brown is a little lighter, more muted, 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.
See Viper Brown on the colour wheel See Rust Orange on the colour wheel
All matches: Viper Brown equivalents · Rust Orange equivalents