Medium Flesh Tone vs Barren Yellow

How close are they?

ΔE 9.2, close: similar, with a visible difference side by side. Barren Yellow is a little darker than Medium Flesh Tone.

Can I use Barren Yellow instead of Medium Flesh Tone?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Barren Yellow is a little darker than Medium Flesh Tone.

Can I use Medium Flesh Tone instead of Barren Yellow?

The same difference applies the other way round: Medium Flesh Tone is a little lighter.

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.