Board Thread:General Discussion/@comment-27907368-20160323193924/@comment-27620479-20160509155900

The white soul color stands for compassion. That's why monster souls react to intentions (have less resistance against a cruel opponent's attacks for example), and can only recognize someone as a human, if they, well, have some level of humanity.

Also, that there are more primary traits with their own colors, than presented in the game.