Aquamarine vs Meredius Blue

How close are they?

ΔE 7.9, close: similar, with a visible difference side by side. Meredius Blue is a little darker, more saturated than Aquamarine.

Can I use Meredius Blue instead of Aquamarine?

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

Can I use Aquamarine instead of Meredius Blue?

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