I don't get this one........?

A dumb blond was really tired of made fun of, so she decided to dye her hair so she would look like a brunette. When she had brown hair, she decided to take a drive in the country. After she's been driving for a while, she saw a farmer and a flock of sheep and thought, "Oh, those sheeps are so adorable!" She got out and walked over to the farmer and said, " If I can guess how many sheep you have, can I take one home?" The farmer being a bit of a gambler himself, said she could have a try. The blonde looked at the flock and guessed, "157." The farmer was amazed- she was right! So the blonde (who looked like a brunette) picked one out and got back into her car. Before she left, the farmer walked up to her and said "If I could guess the real color of your hair, can I have my dog back?"