If you're using some kind of processing software, it should give you an RGB reading on any point in the image. The background would show much higher R and B values and even the fur, which probably should be fairly neutral to maybe very slightly reddish would have at least a large B value. If you're serious about the color blindness, you might need someone's help to spot check images.
Extremely cute pup and good shot generally. My only quibble (other than WB) is that I'd rather see more room on the right so the whiskers aren't cut off and there's more room in the direction he appears to be looking (although it's a little hard to be sure).