Plus the reality that a % of males are red color blind, probably makes the yellow even safer.
I posted before about my wife and I being at Bodega Bay on the south ocean Doran beach side. Some blue yaks came out from the harbor/bay to our west and went into the ocean, headed east and immediately disappeared from our sight about a half of a mile away. My eyesight is 20/10 and my wife's is 20/20 with her contact.
They came back into view about 300 yards away to the west and continued on an Eastern course. When they got about 300 yards east of us, they disappeared again. This is a busy bay/harbor and a lot people in boats are moving in and out of the harbor.
Our older son has a fast and powerful boat that he uses in our Delta and the San Francisco bay, and he has incredible eyesight and no problem with any color. He has said that blue yaks and green yaks present a problem in seeing them. He sees yellow first, and yellow yaks stay in his vision longer.
White yaks in an ocean environment, when capsized are apparently very hard to distinguish from ocean white caps. As per a previous posted here by a member, who has flown ocean rescue missions.
A new acquaintance, who does a lot of after market things with yaks agrees with the above re safe color. He is getting into interior color of yaks and impact of color on temps in side the yaks on warm days on those in the yaks. Red is apparently the hottest due to UV reflection. We have noticed that our Red Oasis on sunny/warm/hot days can get very hot. We often put our feet into the water to cool off as well as getting our hats wet and wetting our face to cool down.
My new Freedom Hawk Pathfinder which should be heading west this month will be yellow, and my wife bought some Under Armour yellow outer wear for me. I intend to use this yak for fishing in relatively open areas on local rivers and lakes. Being seen is a priority. I only use my green Freedom Hawk 12 on a speed control lake and in a local river area where the speed limit is supposedly 5 mph. On the river in isolated areas, we still have idiots in boats doing high speeds. Fortunately, the upper river where I go is loaded if snags, submersed logs trees and a few boats that didn't make it.
On the ocean here in Hawaii, we can see the yellow Hobie AI's and TI from twice as far as the red ones.