To get rid of banding, use a color depth of at least 16 bits per channel and render at a high bitrate when encoding your video. You can also use color noise, in color mode on top of the footage, you might want to decrease the saturation a bit to make it less noticeable.
Banding visible:

Banding invisible because of noise:

To integrate elements better with their background, you can create a mask of that element, apply it to a duplicate of that background, and lay it over the element with a blend mode of you choice.

Never forget the real secret elements from a real photo/video: noise, chromatic abberation, motion blur, blur/bokeh, vignetting