Let me say, none of you know what your talking about. As for shading with other programs it will look sloppy if you have not had the experience with colors from a basic program. You can't go from nothing to advanced and expect to be great. You can go from basic to advanced.. and be great but it would take time. ms paint teaches you outlines and basic coloring. Neo Paint does the same. If you go to adobe you just use filters and blur tools you won't learn diddly squat. You have to be up close and personal with it.
If you did not use adobe photoshop for that garage door, then sir you need a hell of alot more practice with coloring. The lines in the door look like they were just placed on there.. there is no light changes so it seems like its not real. New to graphics? try to use only 5 different colors excluding black. so you understand light
