Yellow vs Lemon Yellow

How close are they?

ΔE 16.4, loose: different enough that you should pick on purpose. Lemon Yellow is noticeably darker, more muted than Yellow.

Can I use Lemon Yellow instead of Yellow?

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

Can I use Yellow instead of Lemon Yellow?

The same difference applies the other way round: Yellow is noticeably 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.