Blonde at store

A blonde walks into a store and sees a t.v. that she wants.  So she goes to the front desk and said "I would like to buy that tv." Then the clerk said, "Sorry, I don't sell to blondes."  She comes back the next day with red hair and she asked for the tv.  The clerk said, "Sorry, I don't sell to blondes." The day after that, she came back with black hair and asked for the tv. The clerk said, "Sorry, I don't sell to blondes" The day after that she came back with green hair and asked for the tv. The clerk said, "Sorry, I don't sell to blondes."  She said, "OK, good job, but how did you know I was a blonde?" The clerk says, "That's not a tv, that's a microwave."