Murder Scene vs Cygor Brown

How close are they?

ΔE 22.1, loose: different enough that you should pick on purpose. Cygor Brown is a little lighter, warmer than Murder Scene.

Can I use Cygor Brown instead of Murder Scene?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Cygor Brown is a little lighter, warmer than Murder Scene.

Can I use Murder Scene instead of Cygor Brown?

The same difference applies the other way round: Murder Scene is a little darker, 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.