I umpired in the minor leagues (not as a replacement, either). I wore black ball bags my entire minor league career. Being in the minors, that obviously meant I wore them with a navy pullover shirt.
As an aside, a brief viewing of the pictures at:
http://www.umpirepictures.com/
showed that some of the IL umpires last season wore a black ball bag with their navy shirt, and some wore blue.
Also, I was never deducted on any evaluation for wearing black ball bags.
Simply put, you are 100% incorrect in stating that black ball bags are innappropriate with a navy shirt. Quite the opposite, the black bag was the bag of choice for many MiLB umpires.