Gobi Brown vs Dark Yellow

How close are they?

ΔE 18.8, loose: different enough that you should pick on purpose. Dark Yellow is noticeably lighter, much more saturated, cooler than Gobi Brown.

Can I use Dark Yellow instead of Gobi Brown?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Dark Yellow is noticeably lighter, much more saturated, cooler than Gobi Brown.

Can I use Gobi Brown instead of Dark Yellow?

The same difference applies the other way round: Gobi Brown is noticeably darker, 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.