I've leased a farm with a block barn. The stalls are painted white. How on earth do you keep your stalls clean? I must have messiest horses, because right now it looks like I better plan on pressure washing every week or it will look terrible.
I'm considering repainting the bottom half of the stalls a color that will hide the dirt better, but short of that, I'm lost.
I guess if the looks are going to bother you, the weekly pressure washing is going to be part of your routine.
White is nice because it gives more light back, but other colors of paint might be easier to live with if the stains don't show so MUCH in contrast.
I do know white walls seem to draw in flies who leave LOTS of nasty stuff behind. This from dairy barns as a kid. They got white painted every year, and each summer the flies would discolor the walls. That doesn't wash off easily, but we didn't have power washers then either. Just being visible fly dirt was yucky, bothered ME!
Horses are going to have stained walls in any kind of barn. New grass to graze will make it worse! Wood stall stains must just not be quite so visible. I wouldn't be washing my walls weekly to keep the stains gone, especially if I didn't have new horses coming and going that might be carrying something. Too many other things to do that HAVE to be done in a timely fashion.
If manure staining bothers you greatly, I would repaint the walls another color. Plus you would probably have a lot less flies with darker shades inside the barn, horses would be more comfortable not being chewed on. Might need to add a few light fixtures, but probably worth it in time saved from all that power washing.