What does everyone use for white markings?! 

i used this as a shampoo when i had a grey https://www.chobhamrider.com/collections/horse-health-grooming-shampoos/products/supreme-blue-shampoo

and then this for white markings on my horses with white markings https://www.chobhamrider.com/collections/horse-health-grooming-shampoos/products/naf-brighter-than-white-whitener 

Thanks!  I'll take a look!

No worries hope it's some help for you