Sapphire Blue vs Mahogany Ink

How close are they?

ΔE 41.5, loose: different enough that you should pick on purpose. Mahogany Ink is noticeably darker, more muted, warmer than Sapphire Blue.

Can I use Mahogany Ink instead of Sapphire Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 41). Mahogany Ink is noticeably darker, more muted, warmer than Sapphire Blue.

Can I use Sapphire Blue instead of Mahogany Ink?

The same difference applies the other way round: Sapphire Blue 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.