Soul Beast
Something about developing one's undead soul is that it reveals and empowers aspects of your inherent soul. Two major aspects that I discovered about my soul were soul color and rigidity or flexibility.
Starting with soul color, it says things about your personality as well as what you're good at. A person with a red soul may be quick to anger but they might also have a strong and indomitable will. The red could also indicate they excel at blood manipulation.
Whereas a person with a black soul may be secretive and untrusting of other's intentions, but they may also be really good at keeping others secrets and have a strong sense of loyalty. The black could also indicate they excel at stealth and shadow manipulation.
Now what does a white soul say about a person? One would initially assume purity and good intentions, but what if that soul has other features?