Hexos Palesun vs Dark Yellow 2

How close are they?

ΔE 23.5, loose: different enough that you should pick on purpose. Dark Yellow 2 is noticeably darker, warmer than Hexos Palesun.

Can I use Dark Yellow 2 instead of Hexos Palesun?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Dark Yellow 2 is noticeably darker, warmer than Hexos Palesun.

Can I use Hexos Palesun instead of Dark Yellow 2?

The same difference applies the other way round: Hexos Palesun is noticeably lighter, 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.