i agree with alot of vipertheninjakitten's critique. as for angelic wings, they sould be going upwards and with a slightly sharp point at the tip, but not to sharp that it could rip my eye out o.o'

for demonic wings, they sould go down and have alot of sharp points signifying devil and satan.

the horns are a little too long, and a little too pointed up at the end.

the variety of colors is very nice and the light side does contrast alot with the dark side, but the green on the angelic side is a little too uneven with the other side. a light blueish green could work, same with the gray on the side of the angelic side. there could be a little more red on her angelic side.

for the character, try to use a little bit brighter colors for the outfit rather than use custom colors. the demonic side could use a little bit of darker clothing. ex: the top. for a demonic ((evil)) chick, she has a pretty, sky blue top ^.^ and a bit darker green eyeliner ((or whatever XD))

i'm in a strict film studies class, so i hope i made sense...a little ><'