Instead of wearing the white sleeves that his team is supposed to use, Brown's were colored red. It's kind of surprising that Brown would get fined for wearing red, since it's one of the 49ers' primary colors.
We actually found out that Brown was fined for wearing the unacceptable sleeves because he surprisingly posted his official letter from the NFL to his Twitter account as a photo (via Matt Maiocco of CSNBayArea).
You can blame the league for being too harsh on silly matters like what color players' pads, socks, or other clothes are, but the only person to blame in this situation is Brown. There's absolutely no excuse for this, especially from a veteran with six years of NFL experience.
If Brown was confused at all about what color sleeves he was supposed to wear, he should have asked a coach or the team's equipment manager. He also could have looked at the white-colored sleeves that his teammates were wearing.
These are the rules that the NFL must get really frustrated over when they are broken because they are so simple to follow.
Fining a guy $5,250 for violating this kind of rule is also going to anger the fans, because they want the league focusing on making a deal to get the real referees back onto the field and not dealing with a player's choice of sleeves.
With multiple players in the NFL having been spoken to about what they have worn on the field so far this season, we might finally see the number of these types of fines decrease going forward.