Tidal Blue vs Silver Grey

How close are they?

ΔE 20.5, loose: different enough that you should pick on purpose. Silver Grey is much more muted, cooler than Tidal Blue.

Can I use Silver Grey instead of Tidal Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Silver Grey is much more muted, cooler than Tidal Blue.

Can I use Tidal Blue instead of Silver Grey?

The same difference applies the other way round: Tidal Blue is 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.