Fulgurite Copper vs Life On Mars

How close are they?

ΔE 21.5, loose: different enough that you should pick on purpose. Life On Mars is noticeably darker, cooler than Fulgurite Copper.

Can I use Life On Mars instead of Fulgurite Copper?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Life On Mars is noticeably darker, cooler than Fulgurite Copper.

Can I use Fulgurite Copper instead of Life On Mars?

The same difference applies the other way round: Fulgurite Copper is noticeably lighter, 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.