You can get some regular Laundry Blueing at the grocery store and add a little to regular horse shampoo. It works great. Makes manes and tails sparkling white and just costs a tiny bit of what some products cost.
Hey, do you guys know if these techniques work to lighten dapple grays? I just started working with a Dappled Gray Percheron/Arabian cross and he quite stained. I want to lighten him up without messing up his beautiful dapples. He needs to grow his mane out too but I'm not going to worry too much about that at this point.
Here is pic for you to see what I'm talking about. He's really dirty in these pictures too but a lot of it is staining.
I've heard that putting corn starch/something like that on white spots for SHOWS gets white markings even whiter, and for special occasions you could probably use it to get a few grass stains out of their coat, but I don't know how good that would be for every day. Also, for growing out/thickening manes and tails? It helps if you don't brush them daily, just use a bit of oil and rub it through on bad hair days to get the tangles out, and just finger comb it. Brushing or combing them daily causes breakage and will just THIN the hair. Your horse is beautiful, btw.