ΔE 13.2, fair: the same colour family, but not a straight swap. Niblet Green is noticeably darker than Kraken Skin.
Can I use Niblet Green instead of Kraken Skin?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Niblet Green is noticeably darker than Kraken Skin.
Can I use Kraken Skin instead of Niblet Green?
The same difference applies the other way round: Kraken Skin is noticeably lighter.
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.