Havesomeseichel,
Do you think that someone who wears a wrinkled white shirt will automatically have a pressed neat shirt if it is blue? The same way a person can wear a blue shirt, he can wear a white shirt if that is what everyone in the yeshiva is doing. (No, do not kick him out, or belittle the person, just be aware that he is making a statement by dressig differently)
Why don’t we turn it around and compare a pressed white shirt and dark dress slacks and leather shoes as compared to a grungy t-shirt, ripped faded jeans and flip flops?
It seems that it is much more likely that a person who dresses down will wear less b’kovodik clothing then they would when dressed up. Look at so many respectable buisnessman who wear expesive suits and clothing yet when they dress down will wear clothing as described above.
If you have issues with someone looking slobby, it is most likely that the person is not neat and not that wearing a white shirt make him look like a slob.
As far as the fellow in the picture feeling bad, it is an old picture that was printed many times with the blue shirt. The bochur in the picture may even have grey hair at this point, that is how old the picture is. I hardly think he cares, if he even knows. But I may not be a sensitive as you.
Midwest 2, I have a very difficult time believing your story that “in a lot of cases it starts with a blue shirt. The R’Y comes down on the boy, who had no idea he was committing such a heinous aveirah. So, he figures, why shouldn’t I commit more if I’m going to get put in herem anyway?”. The truth is very likely the opposite, that the child started wearing different clothing than the others as a sign of rebellion or to excluded from the rest of his classmates.