Are deer invisible to dogs because of color-blindness?

I know that sounds like a dumb question, but I have a bet hound and a lot of deer walk around our suburban neighborhood in broad daylight and he acts like he can't see them. I know he can see squirrels and chipmunks, but it's like a big deer is invisible. Are dogs color-blind? A reddish-brown deer against green gr - does it not show up for them? He doesn't bark, I don't think he will even look at them.