I love Hi Viz! I have a coat, full chaps, tabbards and chest bands for my horse.
I also think that it depends on the season (and colour of leaves on the hedges etc) what colour Hi Viz is most effective so have a lovely selection of yellow, orange and pink! Much to my husband's amusement!
However, I have found that my horse doesn't seem to object to be me being dressed like this although I do wonder if my hacking partner needs sun glasses to deal with the brightness! Fortunately she is also a keen Hi Viz fan.... if wearing Hi Viz you give drivers extra time to stop - to put this in perspective this can be translated as the length of a dressage arena.