I use Gold Label Mud Guard which is amazing - mud literally just slides off. I use it all the time at home as well on a coloured horse with pink skin and we live in the vale. So far so good. Have used it for years and no horse has had mud fever or any kind of mud rash.
We have always used pig oil (when we can get it) and if none of that baby oil works well too.
I apply it with a flannel all over the legs and under the tummy. Mud slides off.