Horse changed 3 times during the race
So, during the race in the finale I have now seen Rosie on several different horses - at around 31 minutes - starts with a darker horse with just a small star. Then a more chestnut with a wide blaze, then a star and a very narrow blaze. In the winner's circle she seems to be on a horse that has a straight blaze without a star at the top. It's most noticeable when she goes from star only to the wide blaze when Mongateau first starts to pull out of the pack.
Did they not think horse people would be watching and notice this? That everyone would just be looking at silks? At least paint the horse to have the same face markings, especially when it's the focal horse. That's just lazy.