Rigor Mortis vs Phoenix Egg

How close are they?

ΔE 21.1, loose: different enough that you should pick on purpose. Phoenix Egg is noticeably lighter, warmer than Rigor Mortis.

Can I use Phoenix Egg instead of Rigor Mortis?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Phoenix Egg is noticeably lighter, warmer than Rigor Mortis.

Can I use Rigor Mortis instead of Phoenix Egg?

The same difference applies the other way round: Rigor Mortis is noticeably 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.