Dogs can make out yellow and blue, and combinations of those colors. This renders a lot of the world grayish-brown. That lush green lawn? It probably looks like a field of dead hay. That bright red velvet cushion? Still comfy, but it probably comes across as a dark brown blob to the dog.
Dog Vision offers an online tool to help you see things as your dog sees them. There are also apps that you can use to see what your dog is seeing at any time.