Magic Blue vs Frostheart

How close are they?

ΔE 9.6, close: similar, with a visible difference side by side. Frostheart is a little lighter, more muted, cooler than Magic Blue.

Can I use Frostheart instead of Magic Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Frostheart is a little lighter, more muted, cooler than Magic Blue.

Can I use Magic Blue instead of Frostheart?

The same difference applies the other way round: Magic Blue is a little darker, 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.