DeeDee,
OK, you can set your flash exposure by putting the meter where the dog is going to be and triggering your strobes. That will tell you what the f-stop is at the point where the dog will be. It shouldn't matter that much which background you're using since it isn't absorbing the light that's falling on the dog. The difference will be how light or dark the backdrop is in relation to the subject.

As for the difference between Goldens and Newfies, I really don't see much in practical terms when I shoot a show and seldom change my f-stop. Given the dynamic range of CMOS sensors in the Canons I shoot, I can expose for Goldens and still not blow out Samoyeds nor have any problem bringing up Rotties. Post-processing is where it all happens so as long as my initial exposures are close to being spot on, I don't have any difficulties.

One other small detail is the fact that I use silver umbrellas on my strobes which tends to highlight black dogs better.

Yes, shooting available light indoors is truly a challenge and in many venues, you'll get the cycling effect both with flourescents and with carbon arc lights. My friends who shoot Agility events go crazy at indoor facilities since they can't use flash and the lighting is variable not just in terms of color balance but also in terms of actual illumination. I've never had a problem (knock on wood) at the Conformation shows where I've shot candids -- and that includes at the AKC/Eukanuba shows and at Westminster. But you need to be aware it can happen and you need to test for it when you arrive at the site.

I was in Perry, GA last week and was asked to shoot a black Standard Poodle for one of our advertising clients. They wanted candid ring shots. One of the other handlers asked me to shoot her white Standard Poodle as well. Both were Specials so they were in the same ring and the same time. Indoors. Lousy lighting. ISO 1600. So I had no choice but to shoot RAW, even though it limited the number of frames I could shoot in motor-drive mode for the moving shots. I was able to get some usable shots but it was definitely a challenge in post-processing.

I guess that's why we enjoy this stuff so much: it isn't just the fact that we're shooting subjects we really love but the fact that we can deal with all the technical problems and still manage to add in some creativity.

Jim