The nice thing about black is that it doesn't show cycling dirt and grease. Try changing a tire in the rain or repairing a chain in full hi-viz and you'll need half a bottle of Shout to get the grease out. And nothing looks stupider than all-red cycling shorts after a couple of months. So that's why people wear black IMO.

OTOH, I used to wear blue and green jerseys until a motorist pulled out right in front of me because he didn't see me. I had time to lock up the rear and lay the bike down as I hit him, so just a little blood. I don't wear anything except bright colors now so I just use the Shout. I haven't had that happen again. I just hate riding with people who are the same color as asphalt. They are a danger to everyone. And judging from the small sample of my riding friends, they do get hit. I'd rather take more trouble with my laundry, thanks.