The white robes with hundreds of tiny black spots?

That's a cool association, I never considered that- reality is a little more morbid, though. Those cloaks are actually made of hundreds and hundreds of ermine (stoats in winter fur), every one has snow-white fur and a tiny black tip on its tail. Some artists don't want to pant out every individual pelt, though, so just do a big white cape with spots.

The ermine represented purity, nobility, royalty, etc. A famous story being that an ermine, while being pursued by a hunter, stopped at a muddy bank and gave itself up for death rather than soil its beautiful fur.