Abyssal Blue vs Silver Grey

How close are they?

ΔE 18.4, loose: different enough that you should pick on purpose. Silver Grey is noticeably lighter, much more muted than Abyssal Blue.

Can I use Silver Grey instead of Abyssal Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Silver Grey is noticeably lighter, much more muted than Abyssal Blue.

Can I use Abyssal Blue instead of Silver Grey?

The same difference applies the other way round: Abyssal Blue is noticeably darker, much more saturated.

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.