Vivid Flesh vs Pixie Pink

How close are they?

ΔE 30.7, loose: different enough that you should pick on purpose. Pixie Pink is more saturated, cooler than Vivid Flesh.

Can I use Pixie Pink instead of Vivid Flesh?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 31). Pixie Pink is more saturated, cooler than Vivid Flesh.

Can I use Vivid Flesh instead of Pixie Pink?

The same difference applies the other way round: Vivid Flesh is more muted, 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.