Has anyone else noticed that the Aeons glow light and dark?

I have always wondered what it meant or if it is just my eyes playing tricks on me. Back when it was on the PS2 my friend said it was because Yuna got strong enough that the Aeons where slowly becoming Dark Aeons before becoming Light Aeons (Max Stats.)

I instantly thought he was pulling my leg because why would your Aeons become Dark Aeons before becoming Light Aeons. But I have always wondered why they glow and just though if someone might know.