Ocean Depths vs Greatcoat Grey

How close are they?

ΔE 16.5, loose: different enough that you should pick on purpose. Greatcoat Grey is much more muted, warmer than Ocean Depths.

Can I use Greatcoat Grey instead of Ocean Depths?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Greatcoat Grey is much more muted, warmer than Ocean Depths.

Can I use Ocean Depths instead of Greatcoat Grey?

The same difference applies the other way round: Ocean Depths is much 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.