Bordeaux Red vs Mephiston Red

How close are they?

ΔE 16.3, loose: different enough that you should pick on purpose. Mephiston Red is a little darker, much more saturated than Bordeaux Red.

Can I use Mephiston Red instead of Bordeaux Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Mephiston Red is a little darker, much more saturated than Bordeaux Red.

Can I use Bordeaux Red instead of Mephiston Red?

The same difference applies the other way round: Bordeaux Red is a little lighter, much 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.