ΔE 12.3, fair: the same colour family, but not a straight swap. Ivory RLM05 is a little lighter, cooler than Tan.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Ivory RLM05 is a little lighter, cooler than Tan.
The same difference applies the other way round: Tan is a little 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.
See Tan on the colour wheel See Ivory RLM05 on the colour wheel
All matches: Tan equivalents · Ivory RLM05 equivalents