Pallid Bone vs Mummy White

How close are they?

ΔE 27.3, loose: different enough that you should pick on purpose. Mummy White is noticeably darker, more muted, warmer than Pallid Bone.

Can I use Mummy White instead of Pallid Bone?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 27). Mummy White is noticeably darker, more muted, warmer than Pallid Bone.

Can I use Pallid Bone instead of Mummy White?

The same difference applies the other way round: Pallid Bone is noticeably 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.