Orchid vs Pixie Pink

How close are they?

ΔE 18.8, loose: different enough that you should pick on purpose. Pixie Pink is a little lighter, warmer than Orchid.

Can I use Pixie Pink instead of Orchid?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Pixie Pink is a little lighter, warmer than Orchid.

Can I use Orchid instead of Pixie Pink?

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