Interesting topic this.
I suggested some time ago on another forum that seeing something red or yellow out of the corner of your eye could be distracting. I think at the time it was someone in a red shirt that I'd seen.
I got completely flamed for suggesting that people should consider carefully what they are wearing to watch at a race meeting.
I've even seen red/yellow striped umbrellas that at a distance that looked like an oil flag.

Stuff like that has always caught my eye don't ask me why.

We constantly hear of camera flashes being distracting but they have never bothered me. Then again not many are trying to take my picture

I did once make the mistake of using a spectator (he was wearing a bright blue coat) as a braking marker at the Steam Packet races about 10 years ago. All race he was there until the last lap I ran into the bales :roll: trying to get stopped