Blossom, the oldest of the Powerpuffs, has a pink color scheme and is the leader of the group. Although the sisters technically weren't born but created, they are all the same age, but Blossom does still read as the unofficial "Older sister" of the group. I often imagine in the "sugar, spice, and everything nice" recipe, Blossom possessed the majority of the latter. She comes across as the most well rounded and therefor well-adjusted character. Insinuating that maybe her main ingredient contains a complexity (everything) that her fellow puff sisters do not.
Buttercup is the green-schemed bad-girl of the group. The quintessential middle child (if there technically was one), Buttercup takes no prisoners. and no π€«. Buttercups demeaner can often come off as aggressive, and to some, off-putting. The three girls are made of sugar, spice, and everything nice. The acknowledgement that spice would be a rageful character is actually a quite subversive choice for a childrenβs show. Creating a character that represents young girls and personifies anger allow those same girls to make space in themselves for their own anger.
Bubbles, as you can imagine, is the unofficial youngest child. She has a bubbly disposition, hence the name, and, despite them all being canonically children is written as the most "childlike" of the Powerpuffs. She also loves her stuffed octopus. Perhaps this is an easter egg referencing a deeper intellect that Bubbles has. Perhaps she is the octopus, a creature whose intelligence was disregarded because of the vessel it came in. Maybe she just thinks their cute.