Abyss Blue vs Deep Blue

How close are they?

ΔE 6.2, close: similar, with a visible difference side by side. Deep Blue is a little darker, more muted than Abyss Blue.

Can I use Deep Blue instead of Abyss Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). Deep Blue is a little darker, more muted than Abyss Blue.

Can I use Abyss Blue instead of Deep Blue?

The same difference applies the other way round: Abyss Blue is a little lighter, 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.