I have heard that so much, and I can't believe it. I saw a video once where a man was determined to prove that wrong, and he did. He taught the dog to fetch different colors of cups. Why he used cups I have no idea, but he told the dog to go and get the blue cup, and then the red one, and the green, so on and so forth.
Just when you thought that it knew which cup was where, he mixed them up, and set the dog out to do it again. I was taken aback at this, the dog brought the right cup every time! So, no, I don't think that they are colorblind. Hope this helps, good luck.

 Okay well they are color blind but, the cup thing is each cup as a different smell that's how the dog figured it out. Also there are different shades of the black and white like gray and lighter and darker shapes that also help the dog

 Yes, I've bred dogs for 20 years. Dogs are color blind. Ask your vet.