Taste? Hell, from what I've read, all you taste is in your mouth!
Obviously, I disagree with your assessment. A properly worn, well maintained uniform is what makes the umpire look professional. Yes, some colors make it difficult, but I don't believe navy blue is one of them.
Also, as Steve M noted, the navy is much more forgiving. How professional does it look when an umpire is wearing grey and sweating like a bottle of cold water in the desert?
I don't necessarily disagree with your view of the jacket with the navy and I really don't have an answer to a possible change.