I don't have a smart phone, so I can't answer your question about colour saturation. My apologies.
I CAN however say that this is a pretty nice piece of work for being made with only a single finger. :P
The lighting seems consistent with a forward on light source...
Might want to add just a tiny bit of torch light on Skeletrons' right arm if you ever revisit this particular piece of work.
Perhaps even add a few more details on the spider webs and I think you've got a fine piece of art here...good work!
(On a side note, the terraria bosses would look absolutely HORRIFYING in real life...:P )