I've just been sworn at by a rider on a local lane. She was riding a bay horse, wearing black and navy. It's raining and dingy out, and she had pulled into the verge so she was against the hedge. She was practically invisible. I was doing all of 25 mph, and I stopped as soon as I saw her.
Now, we have ponies, and DD doesn't leave the yard without a fluorescent vest, martingale, tail wrap, leg wraps and bridle. I know I'm a bit excessive, but this matters! fluorescent gear means that an average, drivers see you three seconds earlier, When someone is doing forty, that is one hell of an advantage! If you ride in high flight areas near military bases, as we do, it means the difference between a twin rotor chinook flying low overhead, or diverting round you. According to a report I read, horses are unable to distinguish fluorescent stuff, and there really isn't an excuse! It's not about you or your horse, it's about drivers, being able to see you!