User blog comment:WeissSchnee/Adam's Aura/@comment-23784953-20130826002050

This is just speculation but... red parts around his clothing glowed when he did that.

Notice Crimson do the same when casting her spell.

I think it's not just the person that glows when they start activating their aura, but a certain aspect of what they're wearing. Heck, possibly even Yang's hair burning up is a side effect of her aura.

If we take this theory further, an aura affecting their outfit will also explain Ruby's rose petals.