Sand Golem vs Estus Yellow

How close are they?

ΔE 27.4, loose: different enough that you should pick on purpose. Estus Yellow is noticeably lighter, cooler than Sand Golem.

Can I use Estus Yellow instead of Sand Golem?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 27). Estus Yellow is noticeably lighter, cooler than Sand Golem.

Can I use Sand Golem instead of Estus Yellow?

The same difference applies the other way round: Sand Golem is noticeably darker, warmer.

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.