I'm definitely hoping we're allowed to dye Job armors as well! Though, I will say, I do understand how some may feel that seeing White Mages in anything other than white-colored clothing to be a bit strange at first. Still, for me, the red accents is the biggest and most important part of a WHM design. I did a quick color mock-up for WHM, MNK, and PLD.
The example at the end shows what a possible mixing and matching may look like (I wasn't sure if the hood was the actual head piece or if it's part of the body piece). Now, a blue-colored cloak may not exactly seem very WHM, but I think shape/silhouette and design will make up for that. Each Job armor has very unique and recognizable shape/design that I feel color won't distract from.
MNK:
Not pictured in this picture are the pauldron pieces, but still, a very strong and recognizable silhouette.
PLD:
It's interesting to note that in Japan, the Paladin is actually called Knight. So I personally see no problem in seeing one in dark-colored armor.
I do so hope SE will allow us to customize color for Job armors. I think it'd be fantastic to have that option there for those who want it and of course, for those who enjoy the traditional and classic colors to choose that as well. If it bothers you too much, you're of course welcome to not party with that yellow-clothed WHM or that pink-clad BLM... but I'd hope the community would never come to be like that.