I do think the question about colours of wings is pretty cool. Would make things pretty entertaining if everyone had those varying colours depending on their soul. Though of course no idea what colour my soul would be.
Hopefully doesn't lead to wing discrimination or something.
Transparent (like the clearest of glass). I've come to accept that we all have "positive" and "negative" attributes within ourselves. And I am no exception.
If a soul is something that is separate from your body whilst you are alive, then I think the color would be of a spectrum of color that we could never understand or see. But when you "release" your soul to heaven, or purgatory, ect; I think it would join the entities together that are your loved ones and your new environment, that have no color, or visual light at all. I read a lot of Sylvia Brown. so I think about this stuff a lot... ;p
Because I am a unicorn.... just kidding. Nah, I think I pick that color because despite my routine melancholy nature I have very vibrant sparks of life in me that seem to shine through.