This avenue of experimentation will come very naturally to anyone who has worked and played in a darkroom. Traditional photographic practice will clearly make one highly conscious of the interplay of positive and negative. There is a great deal of expressive possibility in exploring different forms of inversions.
Inversion can be of color, or of tone, or both. Command-I will invert the whole of the selection, both its color and its tone. You can then fade this inversion by choosing Fade > Invert from the Edit menu to give you many more options.