The shirt doesn’t make the man into a yeshiva bochur. Anyone can wear a white shirt. It’s the man fills the shirt.
Thank goodness there are still a few yeshivas out there in the velt that can see more in their bochurim then the color of their shirts. My son’s dress code is for “conservative” button down shirts. That’s where the blue often comes in.
Years ago, when my husband was there, guys wore color shirts at Mirrer. They’d probably be kicked out now.