I don't care what color a horse is, I was having a problem with horses on Mondays for a while. Big accidents on Mondays, but then it was usually a tack issue, so now I don't ride in anything that doesn't fit and I generally don't ride other people's horses until I re-start them myself first (especially if they are "fresh off 30 days training" by somebody else).

Gotta use some commons sense, if a horse is wanting to move off before you get on there is a big red flag. I remember skittering along clinging to the sides of OTTBs fresh off the auction lot and scrambling up and holding on while the horse bolts sideways through jumps and bounces off the arena fence. That was just dumb, obviously unsafe and didn't necessarily do the horse any favors. I will not get on that same sorta horse now until I fix the problem. Or a horse that is visibly in some sort of discomfort from lameness, back pain, poor saddle fit etc. I don't ride those horses anymore, not fair to them until their discomfort is sorted out.

If I know a saddle doesn't fit a horse or if he is sore and I get on anyways and there is a problem it is 100% my own darn fault, serves me right for being stubborn or stupid in not acknowledging the situation. Horses are so patient and forgiving that people get away with a lot of crap they shouldn't be able to get away with.