Naphthol Red Medium vs Ink Magenta

How close are they?

ΔE 37.4, loose: different enough that you should pick on purpose. Ink Magenta is noticeably darker, much more muted, cooler than Naphthol Red Medium.

Can I use Ink Magenta instead of Naphthol Red Medium?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 37). Ink Magenta is noticeably darker, much more muted, cooler than Naphthol Red Medium.

Can I use Naphthol Red Medium instead of Ink Magenta?

The same difference applies the other way round: Naphthol Red Medium is noticeably lighter, much more saturated, 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.