Funny Blonde Joke

A blonde walks into an appliance store and sees a TV she'd like to buy. She goes to the register and says, "I wanna buy that TV." The man says, "Ma'am, I'm sorry, we don't sell to blondes."
The blonde walks out and dyes her hair brown. She comes back in and say, "I wanna buy that TV." The man gives her a look and says, "Ma'am, I've told you, we don't sell to blondes."
So she walks out and dyes her hair black. She comes back in and says, "I wanna buy that TV." The man gives her another look of pity and says, "Ma'am, I've told you three times, we don't sell to blondes."
The blonde walks out and dyes her hair red. She comes back in and says, "I wanna buy that TV." The man gives her a very tired look and says, "Ma'am, I've told you. We don't sell to blondes." She asks, "How have you known I'm a blonde this whole time?"
The man replies, "Because ma'am... that's a microwave."