ΔE 15.8, loose: different enough that you should pick on purpose. Ivory RLM05 is a little darker, much more saturated than Ushabti Bone.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Ivory RLM05 is a little darker, much more saturated than Ushabti Bone.
The same difference applies the other way round: Ushabti 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.
See Ushabti Bone on the colour wheel See Ivory RLM05 on the colour wheel
All matches: Ushabti Bone equivalents · Ivory RLM05 equivalents