Mid Mustard Khaki vs Dark Yellow

How close are they?

ΔE 17.1, loose: different enough that you should pick on purpose. Dark Yellow is noticeably lighter, much more saturated than Mid Mustard Khaki.

Can I use Dark Yellow instead of Mid Mustard Khaki?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Dark Yellow is noticeably lighter, much more saturated than Mid Mustard Khaki.

Can I use Mid Mustard Khaki instead of Dark Yellow?

The same difference applies the other way round: Mid Mustard Khaki is noticeably darker, much more muted.

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.