One of my colleagues asked a Chinese girl in her class using the name Rainbow as her English name to change it because it "wasn't a name." While I wouldn't use Rainbow and I find it slightly silly, I don't think it's unusable (and I've seen Chinese students with way more ridiculous English names, like Shoulder and Pineapple). I even like it in a GP-ish way, I'd use it on a pet, for instance.
Thoughts?
"We have to live without sympathy, don't we? That's impossible of course. We act it to one another, all this hardness; but we aren't like that really, I mean...one can't be out in the cold all the time; one has to come in from the cold...d'you see what I mean?”
John LeCarré