Marine Mist vs Medium Sea Gray (RAF)

How close are they?

ΔE 15.3, loose: different enough that you should pick on purpose. Medium Sea Gray (RAF) is noticeably darker, more muted, warmer than Marine Mist.

Can I use Medium Sea Gray (RAF) instead of Marine Mist?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Medium Sea Gray (RAF) is noticeably darker, more muted, warmer than Marine Mist.

Can I use Marine Mist instead of Medium Sea Gray (RAF)?

The same difference applies the other way round: Marine Mist 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.