Fey Pink vs Dark Rose Tan

How close are they?

ΔE 29.1, loose: different enough that you should pick on purpose. Dark Rose Tan is noticeably darker, warmer than Fey Pink.

Can I use Dark Rose Tan instead of Fey Pink?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 29). Dark Rose Tan is noticeably darker, warmer than Fey Pink.

Can I use Fey Pink instead of Dark Rose Tan?

The same difference applies the other way round: Fey Pink is noticeably lighter, 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.