Pastel Yellow vs Aged White

How close are they?

ΔE 17.2, loose: different enough that you should pick on purpose. Aged White is noticeably darker, more muted, warmer than Pastel Yellow.

Can I use Aged White instead of Pastel Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Aged White is noticeably darker, more muted, warmer than Pastel Yellow.

Can I use Pastel Yellow instead of Aged White?

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

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.