Hi. As per your suggestions, I made the following changes:
1) Changed color of the sky.
2) Removed strokes from the background objects.
3) Changed colors of the balls.
Please suggest if I did it correctly or how it should be changed to make it better. Also, let me know how may I improve this design further.
If required, I will work on this design even after the contest's time is over, so that the final outcome is the best.