Sekigahara vs Red

How close are they?

ΔE 16.9, loose: different enough that you should pick on purpose. Red is noticeably darker, more saturated, cooler than Sekigahara.

Can I use Red instead of Sekigahara?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Red is noticeably darker, more saturated, cooler than Sekigahara.

Can I use Sekigahara instead of Red?

The same difference applies the other way round: Sekigahara is noticeably lighter, more muted, 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.