Majestic Fortress vs Kraken Green

How close are they?

ΔE 19.8, loose: different enough that you should pick on purpose. Kraken Green is noticeably darker, more muted than Majestic Fortress.

Can I use Kraken Green instead of Majestic Fortress?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Kraken Green is noticeably darker, more muted than Majestic Fortress.

Can I use Majestic Fortress instead of Kraken Green?

The same difference applies the other way round: Majestic Fortress is noticeably lighter, 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.