Afterglow vs Hykey Yellow

How close are they?

ΔE 16.7, loose: different enough that you should pick on purpose. Hykey Yellow is a little darker, more muted, warmer than Afterglow.

Can I use Hykey Yellow instead of Afterglow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Hykey Yellow is a little darker, more muted, warmer than Afterglow.

Can I use Afterglow instead of Hykey Yellow?

The same difference applies the other way round: Afterglow is a little 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.