Cloud Nine vs Crimson Magenta

How close are they?

ΔE 17.8, loose: different enough that you should pick on purpose. Crimson Magenta is a little darker, more saturated, warmer than Cloud Nine.

Can I use Crimson Magenta instead of Cloud Nine?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Crimson Magenta is a little darker, more saturated, warmer than Cloud Nine.

Can I use Cloud Nine instead of Crimson Magenta?

The same difference applies the other way round: Cloud Nine is a little 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.