Mephiston Red vs Dark Hot Pink

How close are they?

ΔE 31.6, loose: different enough that you should pick on purpose. Dark Hot Pink is noticeably lighter, more saturated, cooler than Mephiston Red.

Can I use Dark Hot Pink instead of Mephiston Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 32). Dark Hot Pink is noticeably lighter, more saturated, cooler than Mephiston Red.

Can I use Mephiston Red instead of Dark Hot Pink?

The same difference applies the other way round: Mephiston Red is noticeably darker, 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.