I also use Mane n Tail shampoo and conditioner. I dilute it and works great. I have light colored horses but fortunately they don't get too dirty, plus after most trailrides they get hosed down to remove any sweat and mud.
I use Silk Therapy on they manes and tails and it works great. (its for people). A little goes a looooong way and as some of you know, I have apps and work very hard to get the tails and manes they have (no brushing or combing, all finger picking).
If I want to brighten up the socks (being a trail rider, not a big priority) I use diluted Shimmer Lights (people shampoo) works just like the horse whitening shampoos.
I often cross over between people products and horse products for my horses, as long as the ph is between 4.5 and5.5 it will not be harsh for them and go for the moisturizing products as horse hair already has high protein content in it , they need the moisture benefits in products.