Medium Magenta vs Light Pink

How close are they?

ΔE 24.1, loose: different enough that you should pick on purpose. Light Pink is noticeably lighter, much more muted, warmer than Medium Magenta.

Can I use Light Pink instead of Medium Magenta?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Light Pink is noticeably lighter, much more muted, warmer than Medium Magenta.

Can I use Medium Magenta instead of Light Pink?

The same difference applies the other way round: Medium Magenta is noticeably darker, much more saturated, cooler.

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.