Infernal Red vs Scarlet Red

How close are they?

ΔE 8.0, close: similar, with a visible difference side by side. Scarlet Red is more saturated than Infernal Red.

Can I use Scarlet Red instead of Infernal Red?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Scarlet Red is more saturated than Infernal Red.

Can I use Infernal Red instead of Scarlet Red?

The same difference applies the other way round: Infernal Red is more muted.

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.