Most TMs at my store wear jeans now, and I just don't get the appeal of it. They're cold in the winter, hot in the summer. I often commute by bike, and lemme tell ya, the seams in jeans are all wrong for biking. I have no problem at all finding lots of khakis at thrift stores for cheap, including Dockers that seem like they've never been worn. I so much prefer keeping my jeans for other activities that require tough fabric (yard work, etc.) and my black pants for things like going out with friends.
And plain red shirts are just so easy, also readily available at thrift shops for cheap. One TM at my store frequently wears a burgundy Hogwarts shirt, another a school team shirt that's red, many variations on red which aren't all that close to red. About the only colors I haven't seen are blue, green, and yellow.