Ungor Flesh vs Nickel Azo Yellow

How close are they?

ΔE 15.9, loose: different enough that you should pick on purpose. Nickel Azo Yellow is much more saturated, cooler than Ungor Flesh.

Can I use Nickel Azo Yellow instead of Ungor Flesh?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Nickel Azo Yellow is much more saturated, cooler than Ungor Flesh.

Can I use Ungor Flesh instead of Nickel Azo Yellow?

The same difference applies the other way round: Ungor Flesh is much more muted, warmer.

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.