Skeleton Bone vs Yellow Sand

How close are they?

ΔE 15.7, loose: different enough that you should pick on purpose. Yellow Sand is a little darker, much more saturated than Skeleton Bone.

Can I use Yellow Sand instead of Skeleton Bone?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Yellow Sand is a little darker, much more saturated than Skeleton Bone.

Can I use Skeleton Bone instead of Yellow Sand?

The same difference applies the other way round: Skeleton Bone is a little lighter, much more muted.

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.