You also need to take into consideration that several conure species don't have adult coloration until they are 6+ months old, some may even be 6-8 years old before they get all of their adult colors.
For the most part, dusky and green cheeks are born quite similar to what their adult colors will be like, although they can still change some in color. Since Paco is a hybrid, it's even harder to say what the differences may be between chicks vs adults.
Consider crimson bellied conures. These guys are not born with crimson bellies! But as they mature and molt into adult colors, they get their crimson bellies!
Lets take another look at a different image of Paco....
Notice the red tail feathers??? Then compare that to a maroon bellied conure's tail feathers. Predominantly green/olive in coloration.
https://www.flickr.com/photos/parrots/2729238853/
And if you'd like to examine a maroon bellied closer, you may see that the head and chest area is not similar to Paco at all.
https://www.flickr.com/photos/36917655@N08/4488278918/
Compared to Paco's close up...
You are free to argue that he doesn't look like a green cheek conure either, however, he shares more traits with a green cheek conure than he does a maroon bellied. (re: tail feathers) Body shape is also "off" for a Pyrrhura conure.
If we consider the fact that he is a Pyrrhura x Aratinga hybrid, then it makes sense. He definitely has a dusky head! And there are no large conures with red tails. Only Pyrrhuras have that!
What's interesting about Paco is the fact that other Pyrrhura x Aratinga hybrids (namely Sun x Green Cheek and Nanday x Green Cheek) all have green tails. This makes him unique.
https://www.flickr.com/search/?group_id=1329724@N20&view_all=1&text=green cheek