I've ridden in 90+ degree weather in the past. I've never found them uncomfortably warm, and when the sun is shining bright, can actually be cooler than naked arms.
I can believe the hint about spraying water on them.
Example:
I wore them during a Bike MS (two day 175 mile) ride.
First day it was a coolish day, mid 70s, and POURING during the morning. But as soon as the rain stopped my arms got so cold I actually starting shivering. They dry quickly though.
Next day was in the 80s, 75 miles.
Another Pearl Izumi Sunsleeves user, white (only color I've ever worn).
-mr. bill