Naphthol Red Light vs Ink Magenta

How close are they?

ΔE 21.5, loose: different enough that you should pick on purpose. Ink Magenta is noticeably darker, cooler than Naphthol Red Light.

Can I use Ink Magenta instead of Naphthol Red Light?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Ink Magenta is noticeably darker, cooler than Naphthol Red Light.

Can I use Naphthol Red Light instead of Ink Magenta?

The same difference applies the other way round: Naphthol Red Light is noticeably lighter, 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.