Terracotta Pie vs USAF Tan

How close are they?

ΔE 20.6, loose: different enough that you should pick on purpose. USAF Tan is a little darker, much more muted than Terracotta Pie.

Can I use USAF Tan instead of Terracotta Pie?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). USAF Tan is a little darker, much more muted than Terracotta Pie.

Can I use Terracotta Pie instead of USAF Tan?

The same difference applies the other way round: Terracotta Pie is a little lighter, much more saturated.

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.