Green Blue vs Phantasmal Blue

How close are they?

ΔE 8.5, close: similar, with a visible difference side by side. Phantasmal Blue is a little lighter, more saturated than Green Blue.

Can I use Phantasmal Blue instead of Green Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Phantasmal Blue is a little lighter, more saturated than Green Blue.

Can I use Green Blue instead of Phantasmal Blue?

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