ya, the dark spots need to be darker - if anything it will create some contrast between seperate objects. You don't necessarily have to black line but the range from darkest color to lightest needs to be farther apart. Keep at it!
I'd say there's a good start here, but it's just lacking depth. Although the colors work well together and the application seems tight, the resolution seems to take away from the general quality. Maybe it's alot better, but just hard to tell.
Looking forward to more stuff!