To be fair, dogs know more about flowers than this. We often assume other animals share our emphasis on sight, but images can only scratch the surface of a dog's scent-centric existence.
Still, we know they lack the ocular equipment to see red. Dogs may see a bit like people with red-green colorblindness — albeit blurrier, since they have four to eight times less visual acuity than humans. That's roughly 20/75 vision, meaning dogs lose sight of patterns at 20 feet away that most humans could see at 75 feet.