Tourmaline Alchemy vs Crimson Magenta

How close are they?

ΔE 17.7, loose: different enough that you should pick on purpose. Crimson Magenta is a little lighter, cooler than Tourmaline Alchemy.

Can I use Crimson Magenta instead of Tourmaline Alchemy?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Crimson Magenta is a little lighter, cooler than Tourmaline Alchemy.

Can I use Tourmaline Alchemy instead of Crimson Magenta?

The same difference applies the other way round: Tourmaline Alchemy is a little darker, 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.