Viper Brown vs Quicksand Brown

How close are they?

ΔE 19.2, loose: different enough that you should pick on purpose. Quicksand Brown is noticeably darker, more saturated, warmer than Viper Brown.

Can I use Quicksand Brown instead of Viper Brown?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Quicksand Brown is noticeably darker, more saturated, warmer than Viper Brown.

Can I use Viper Brown instead of Quicksand Brown?

The same difference applies the other way round: Viper Brown is noticeably lighter, more muted, cooler.

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.