Transparent Blue vs Ink Blue

How close are they?

ΔE 7.4, close: similar, with a visible difference side by side. Ink Blue is a little darker, more muted than Transparent Blue.

Can I use Ink Blue instead of Transparent Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Ink Blue is a little darker, more muted than Transparent Blue.

Can I use Transparent Blue instead of Ink Blue?

The same difference applies the other way round: Transparent 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.