Rare stallion facts:

Shining Armor is the only true white pony. They actually had to make the white of his eyes slightly blueish to make his eyes visible against his coat.

Save for a handful of exceptions, the magic aura of a unicorn is a similar color as their iris. Instead of blue, Shining Armor's magic color is magenta. The color of Cadance's eyes. Cadance's magic color is aquamarine, like Shining Armor's eyes. They were destined for eachother.