Why doesn’t MLB enforce uniform rule 3.03(b)?

I am confused by Major League Baseball. Which of the rules are optional?

I refer you to the 2015 Major League Baseball rules, specifically rule 3.03 (b).

Oh and before we begin, the name of the Chair of The Rules Committee is named Sandy Alderson.

Rule 3.03(b) says that undershirts need to be of a uniform solid color for all players on a team.

And yet…

Why is OK for any one player (try to ignore for a second that you like this player, try to pretend it’s Oliver Perez or A-Rod or someone) to ignore this rule while the rest of the team wears blue?

I would imagine the Chair of the Rules Committee would have good command of the rules, and might notice this one.

Now you’re thinking – WHO CARES SHUT UP and all that.  I get it.  I don’t make the rules, I just blog about them.  If the rule is not important then it should not be in there.  But it is.