It is absolutely critical when photographing a dog whose coat is a mix of black and white colors, to set the camera settings to properly expose the file for the white color. Especially when one is using studio lighting.
The reason is to keep the detail in the white part of the dog’s coat. It is true that the black part of the coat will be underexposed and be dark and lack detail. If the camera is set for proper exposure of the black part of the dog’s coat the white will wash out badly with no chance of recovering any detail.
So what can be done? Well, it is in post-production that the fix happens. Photoshop, the great tool that has a function that lets just the black part of the dog’s coat to be lightened to the perfect degree while keeping the white part as it was when the portrait was taken.
This is how I photograph dogs with both colors on their coat and it always works out just fine.