New Brevoort Formspring

At Marvel for many years, blue eyes were the default–absolutely every character had blue eyes, because it was easier in the coloring (one color, rather than a combination of multiple colors that might not register properly, making the character appear cross-eyed.) This changed once the printing technology got better. I don’t know that there’s any such thing behind the DC heroes that you name, I think it was more that, in the era in which those characters were created, dark hair and blue eyes was a sort of shorthand code for a hero–it’s what people expected a hero to look like.