More people use beanies for sun protection than for warmth in the Pacific. They are cooler than hoods in the heat and save people having to slather sunblock on hair challenged heads
By the same token, many people here use hooded vests, or lycra hoods sewn into rash guards as a base layer, more for the back of the neck sun protection than for warmth.
In a lot of open ocean dives in Hawaii, worrying about drifting stinging things during hangs is an issue, so having a hood available to pull up is a pretty useful thing fort that, too.
It's amazing how different the same objects are used in different areas. In Micronesia (Chuuk/Truk, Palau, Yap, etc), full sleeved rash guards are standard wear for sun protection, because very few people have to worry about getting cold. In Hawaii, the same rash guard with a sewn in hood is there to make pulling on a suit easier, and as sting protection.
65 degrees is far too cold for diving. 65 is far to cold for an air temperature. How can you stand walking around when it is 65 degrees? Don't your feet and hands hurt from the cold?