From experience, the best shirts I've found to wear when shooting are the yellow and lime green ones. Yes, it's true, they are not fashion statements but they do get the job done. As a strange person with a camera who is taking pictures you want everyone to figure out who you are, quickly, so they can leave you alone and let you get the shots you need.
At one of the first big accidents I rolled up to with the Press Photographer shirt on, a cop walked up to me and I thought for sure this was going to be the "Get lost" speech we've all heard before. It wasn't. The police officer just asked me to be careful of traffic as I took my shots. The shirt worked like a charm.
In fact by being so bold, as these shirts are, I've never been booted from any scene.
Now commonsense is required; these shirts don't give you a free pass to be disrespectful, rude, obnoxious, or inappropriate. Instead, wear the shirt with pride and be well exposed, in focus, well framed, and evocative.
Since the shirts worked so well for me, I'm sharing them with my fellow freelance press photographers so you can benefit from them as well.
Enjoy!