It s ok to adjust these parameters as long as nothing is fundamentally changed in the photo. For example, if the green frog is changed to blue, that is a fundamental change. If the background is blurred to draw attention to the kitten, that is a fundamental change and not ok. If the shine on Uncle George s bald head is softened to look less like a light-house, that s ok. If Aunt Ethel s red-eye is removed that s ok unless Aunt Ethel has red eyes to begin with.
Digital cameras have a tendency to over-saturate colors.
Most of the time this is ok. There is an effort made to keep a variety of photographic subjects on the site. If ten lady bugs are sent in on ten consecutive days, most likely you will only see one no matter how good the last nine are. But for now, all photos submitted are kept on file. Each photo is considered many times for photo of the day.