All I use is shampoo (special one for grey horses) but to be honest any will do.. just rub it in well and remember that's the only thing about greys.. its impossible to keep them white. The best chance you have is to put a rug on him/her with a neck extension while its being turned out. Not much else you can do im afriad..
Trust me I know. The horse in my avatar picture is my show horse. I do love to bath and groom but it is a pain to keep them clean. I love using the spray on solution EQ solutions. You spray it on and hose it off and it works great.
I can use this product everyday during the summer and it will not dry out his coat. When I show I dod get more detailed and scrub areas that need more scrubbing but other than that I just use the spray on stuff.
I have 2 grey horses and a paint so I know your pain! Haha.
With my riding horse (Romeo) I bathe him and brush everyday. I rub him down with water after rides that he sweats/gets dirthy.
I go through a lot of white horse shampoo.
Light colored horse are fun to keep clean. I honestly hardly ever use a whitening shampoo only because with the EQ solutions I do not need it. Also that stuff dyes my hands and I have a bad reaction to them. If I use a a shampoo I use Orvus.
I've used everything. I mean EVERYTHING. White N Brite, Cowboy Magic products, purple shampoos, blue shampoos... EVERYTHING. I have a box full of 'Crap that doesn't work'.
Then only thing that I've used that does work? WOW Whitener. It uses enzymes to eat away stains, but it's all natural. I groomed the bejeezus out of my gelding, he was still stained, and I used this stuff on him all over, once per day after grooming. I'd wake up in the morning, and like magic, the stains were gone! I've never been able to get him so white before. I'll be buying a lot of this for the upcoming show season.
I just wash my pinto 3 times over before a show & spot clean the day of. I use suave the first 2 times & then quik silver once. I also curry it into his legs & body. It works really well for me. I also try to tie him in the sun afterwards, or at least tie him somewhere so he can't get down & roll before he's dry =D
Alot of brushing. I use regular shampoo to keep my mostly white tricolor clean. I give her a bath the day before the show, the wake up early that morning and bathe her as well.
She dosent really stain, she's never had grass marks, just some poopie stains on her butt. They usually just brush right out after they are dry. The secret is to keep them as clean as possible by brushing as much as you can on problem areas. I don't like to bathe my horses more then once a week.