[Cassandra wouldn't mind them so much if humans in her world didn't react so badly to them.]

I'm... not sure it works that way for us. When a warrior is made, her color is mostly just gone until she dies. A warrior who only loses some will be looked down on, because that means the conversion didn't take properly and she'll be much weaker.

The only way for a warrior to get her color back is to... Awaken. And none of us wants that.