I have a theory about these...

I think the fairies are usually blue because blue is a color that represents tranquility, serenity, and calm. Blue is also the color of the sky, which could be considered as a metaphor/representation of heaven and the beyond, because what is beyond the sky is the cosmos, and the cosmos is what can be considered by many as staring into the face of God. The fairies are almost like angelic beings proceeding from heaven sent by God to assist the protagonists, and God's help through the angel/fairy puts the protagonist at ease, or calm and serenity. Hence the blue color

The pastel colors of the princesses is almost like an earthy essence on the characters. Almost like they are "down to earth". The pastel colors were to almost humanize the characters and promote the values of beauty in modesty and humility. This almost makes them more relatable

The dark, bold colors of the villains is almost a mirror of their personality: power-hungry, egotistical, narcissistic, violent, covetous. As you also mentioned, the red color is the color of aggression and power, which most villains have in spades. But purple, another color you mentioned, is the color of royalty and status, and it represents the arrogance of the villains and their lust to dominate over everyone and everything. Many villains in fact see themselves as entitled to rule and be worshiped as Gods

But yeh, those are some of my takes on your article. A very terrific and insightful article. Very interesting take on what is not often talked about. Kudos