Magenta vs Scarlet Red

How close are they?

ΔE 7.5, close: similar, with a visible difference side by side. Scarlet Red is a little lighter, more muted than Magenta.

Can I use Scarlet Red instead of Magenta?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Scarlet Red is a little lighter, more muted than Magenta.

Can I use Magenta instead of Scarlet Red?

The same difference applies the other way round: Magenta is a little darker, more saturated.

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.