Arctic Gem vs Sky Blue

How close are they?

ΔE 7.0, close: similar, with a visible difference side by side. Sky Blue is more muted, cooler than Arctic Gem.

Can I use Sky Blue instead of Arctic Gem?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Sky Blue is more muted, cooler than Arctic Gem.

Can I use Arctic Gem instead of Sky Blue?

The same difference applies the other way round: Arctic Gem is 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.