Crimson vs Fluid Pink

How close are they?

ΔE 49.3, loose: different enough that you should pick on purpose. Fluid Pink is a little lighter, more muted, cooler than Crimson.

Can I use Fluid Pink instead of Crimson?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 49). Fluid Pink is a little lighter, more muted, cooler than Crimson.

Can I use Crimson instead of Fluid Pink?

The same difference applies the other way round: Crimson is a little darker, more saturated, 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.