Ryza Rust vs Yellow Flame

How close are they?

ΔE 15.0, loose: different enough that you should pick on purpose. Yellow Flame is noticeably lighter, cooler than Ryza Rust.

Can I use Yellow Flame instead of Ryza Rust?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Yellow Flame is noticeably lighter, cooler than Ryza Rust.

Can I use Ryza Rust instead of Yellow Flame?

The same difference applies the other way round: Ryza Rust is noticeably darker, 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.