It's all black with "seasonal ties" usually approved. So, you'll see Flag ties and the occasional Christmas ties. I think where seasonal is concerned they just expect good judgment. Flashing LED's, topless women or giant novelty ties are a no-no!
Worst comes to worst a CP will say something to you. Just don't be wearing it with your North Face Polar Fleece jacket, your backpack and an Ipod in one ear when they see you.
