That is a pretty good observation.I was skimming through 'Preacher' while bored at work and noticed something after awhile. Most of the white characters, or characters in general, are strange and have these massive 'quirks' to them. Jesse, and his friends themselves, are always running into or have history with insane characters.
However, when Jesse runs into black characters, even though they are few and far between in the series, they are relatively normal and usually play an important role in the series. Spaceman, who tells Jesse a lot about his father, offers guidance and some closure for Jesse. Cindy, who he meets in Salvation, is a close friend and reminds him why, even though she's very special, he loves Tulip dearly.
I would even argue, weakly, that the character from the Grail, the man who was in-love with Featherstone, plays an extremely important role and shows the differences in Jesse from the beginning of the series and the end. He is dealt a harsh punishment by Jesse in the beginning but, when he seeks revenge, in the end Jesse shows him kindness and mercy (an act which surprise Tulip). He was even a pretty normal guy and his one 'crazy' character trait was his love for Featherstone. That's all (that I can remember).
I could just be reaching with all this, though.