Incredible first post, This looks amazing, but I think Cam was right, the darkness should ease in more, I think..  I don't exactly know what I'm talking about, but there is probably a way to say that in pixel art lingo.

Awesome thing is that the transparency works perfectly with my background colour! The only thing is that i think the pupil is too dark compared to the rest of the eye. Beside that, its great!

I dig how you're using transparency as one of your shades, hopefully it translates just as well for the many people that use other skins besides the default UI.