I think the algorithm works well because it is a good model of the cognition of our perception, which is in turn a good set of heuristics for coping with sensory data coming from our environment.
Constraining the contrast (the saturation and brightness) to a few ranges reflects the fact that we usually only have to deal with a few different levels of lighting at the same time (for example when going into or coming out of forest, or when the sun is breaking through the clouds).
Limiting the number of colour components to seven each matches the soft limit of our working memory. Whether this is relevent to the vision centre of our brain I couldn’t say, but when we are considering a composition artistically we need a manageable complexity to the hues that it uses.
Producing values that have been structured to fall into ranges that we are neurally predisposed to appreciate may seem like cheating for an artistic program. But in a human this would be called skill, whether that human could account for it or, like AARON, they could not.