ΔE 15.0, fair: the same colour family, but not a straight swap. Sacred Scarlet is noticeably lighter, more saturated than Medium Rust.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 15). Sacred Scarlet is noticeably lighter, more saturated than Medium Rust.
The same difference applies the other way round: Medium Rust is noticeably darker, 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.
See Medium Rust on the colour wheel See Sacred Scarlet on the colour wheel
All matches: Medium Rust equivalents · Sacred Scarlet equivalents