Pastel Peach vs Ryza Rust

How close are they?

ΔE 15.7, loose: different enough that you should pick on purpose. Ryza Rust is a little darker, more saturated than Pastel Peach.

Can I use Ryza Rust instead of Pastel Peach?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Ryza Rust is a little darker, more saturated than Pastel Peach.

Can I use Pastel Peach instead of Ryza Rust?

The same difference applies the other way round: Pastel Peach is a little lighter, more muted.

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.