Dark Kraken vs Viking Grey

How close are they?

ΔE 9.4, close: similar, with a visible difference side by side. Viking Grey is more muted, warmer than Dark Kraken.

Can I use Viking Grey instead of Dark Kraken?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Viking Grey is more muted, warmer than Dark Kraken.

Can I use Dark Kraken instead of Viking Grey?

The same difference applies the other way round: Dark Kraken is 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.