Hansa Yellow Medium vs Deep Yellow

How close are they?

ΔE 15.5, loose: different enough that you should pick on purpose. Deep Yellow is a little darker, more muted than Hansa Yellow Medium.

Can I use Deep Yellow instead of Hansa Yellow Medium?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Deep Yellow is a little darker, more muted than Hansa Yellow Medium.

Can I use Hansa Yellow Medium instead of Deep 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.