I have been quite happy with the natural loop from http://www.customtails.com/ They offer LOTS of different gray options. When I talked to the owner she knew exactly what I would want for hunters, and she asked me to send pictures of my gray's tail so she could match and build it custom for him.
They're really great, tails looked beautiful and very high quality. I would not get anything above 1 lb, I prefer 1/2 pound tails, but that's just me! I also recommend the tapered, and not the blunt cut. Get it a bit longer, so you can have some room to pull up the sides when you French braid it. A tapered cut with a braided tail, no one will ever know you have a fake tail in!
It would be custom to his tail, so I'm not sure if that would be stark white or not. I will attach a photo, but I don't know how. Someone explain please!!
I don't know how to attach a photo either But if it is matched to your horse's tail, I am sure it will look great. I am always surprised that what our eyes tell us is really white is usually not. When I bought a tail that matched my older white horse, it looked so not white when it wasn't on him. When he wears it, it looks white and is a perfect match. I guess that is why I am not an artist
I have no opinions about fake tails other than that if you put one on your horse, please make sure it's on correctly - it looks so dumb when the horse's tail is lifted nicely becuase they are moving well, and the tail is so obviously just hanging down completely seperately. Ugh!
Once in the show ring, my completely unflappable totally bombproof mare spooked when a fake tail fell off the horse in front of us. I think she was scared it might happen to her, too.