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.