Sol Harriman was a Nazi spy who chose a costume and moniker and for some reason chose the name Blue Diamond. It’s not clear why; he has no powers or gimmicks to explain the name. Sure, he’s a Nazi but I’m not certain what nazism has to do with colors or gemstones. Plus, there was already a superhero using the name, and THAT guy had a theme. If he hadn’t been arrested for espionage, they would have pinched him for copyright infringement.
References: [wikipedia.org: Blue Diamond]
[marvel.fandom.com: Sol Harriman]
not[crystal]
Metahuman Database 