This is a checkpoint to make sure you're not detaching the characters from canon just to make yaoi.
If you can't come up with an answer besides "it's funny" you need to try again.
Ok that's all carry on
1. The thesis statement of Yellow's character is "PUNITIVE JUSTICE DOESN'T FUCKING WORK." It's framed as a joke but Yellow's only idea of how to correct any percieved wrongdoings is to inflict punishment upon the person who did wrong. He has no concept of restorative justice, and this lack of understanding hurts himself and the people he cares about. This possibly exists as a reflection of Asgore's own maladaptive mindset regarding his own mistakes, wherein he percieves the divorce as a punishment for what he did wrong; it's not, it's because he was driving himself mad and Toriel couldn't deal with it anymore.
(it's especially reflective of his incarnation in Undertale, where he begins slaughtering the fallen humans to punish the human race; See how the decision ruins his life, and his internal turmoil and regret later on serve as the foundational conflict of his entire character.)
2. A flawed implementation of Justice will always come with a flawed idea of Integrity. It's not just that Blue refuses to pay Green back, it's that he refuses to acknowledge that he owes Green in the first place; if he pretends the problem doesn't exist, he doesn't have to fit it into his framework of Integrity. Blue clearly goes along with Yellow's idea of punitive justice; he helps with the trials, and his assurance to Yellow isn't that he shouldn't be punished, period, it's that he shouldn't be punished because (and ONLY because) he didn't do anything wrong. Blue's view is thus: if you don't want to be punished, you have to present yourself as if you can do no wrong.
We can also link this to Asgore; he percieves his separation from the family was a punishment for whatever happened with the Dark World in the past, and the only way for the punishment to stop is to prove that he was never mistaken in the first place.
In short, Blue and Yellow (perhaps the rest of the flowers, I'd have to examine them all individually) are emblematic of deeply flawed implementations of their associated trait, which can be further linked to the deeply ingrained flaws in Asgore's own mindset and sense of morality, much like how other Darkners (the flowers aren't Darkners, but they're as close as) tend to be reflective of the Lightners who they are owned by and/or bonded to.
