Hansa Yellow Medium vs Moon Yellow

How close are they?

ΔE 6.2, close: similar, with a visible difference side by side. Moon Yellow is a little darker, more muted than Hansa Yellow Medium.

Can I use Moon Yellow instead of Hansa Yellow Medium?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). Moon Yellow is a little darker, more muted than Hansa Yellow Medium.

Can I use Hansa Yellow Medium instead of Moon Yellow?

The same difference applies the other way round: Hansa Yellow Medium 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.