Lemon Yellow vs Space Dust

How close are they?

ΔE 16.1, loose: different enough that you should pick on purpose. Space Dust is a little darker, more muted, warmer than Lemon Yellow.

Can I use Space Dust instead of Lemon Yellow?

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

Can I use Lemon Yellow instead of Space Dust?

The same difference applies the other way round: Lemon Yellow 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.