ΔE 28.1, loose: different enough that you should pick on purpose. Russian AF Blue is noticeably lighter, much more muted, cooler than Summersea Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 28). Russian AF Blue is noticeably lighter, much more muted, cooler than Summersea Blue.
The same difference applies the other way round: Summersea Blue is noticeably 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 Summersea Blue on the colour wheel See Russian AF Blue on the colour wheel
All matches: Summersea Blue equivalents · Russian AF Blue equivalents