Pastel Yellow vs Limelight

How close are they?

ΔE 59.4, loose: different enough that you should pick on purpose. Limelight is noticeably darker, much more muted than Pastel Yellow.

Can I use Limelight instead of Pastel Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 59). Limelight is noticeably darker, much more muted than Pastel Yellow.

Can I use Pastel Yellow instead of Limelight?

The same difference applies the other way round: Pastel Yellow is noticeably lighter, much 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.