ΔE 24.9, loose: different enough that you should pick on purpose. Sapphire Blue is a little lighter, much more muted, cooler than Let Them Eat Cake.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Sapphire Blue is a little lighter, much more muted, cooler than Let Them Eat Cake.
The same difference applies the other way round: Let Them Eat Cake is a little darker, much more saturated, 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 Let Them Eat Cake on the colour wheel See Sapphire Blue on the colour wheel
All matches: Let Them Eat Cake equivalents · Sapphire Blue equivalents