The other day, I was walking in an extra touristy part of a regional tourist town with two coworkers during a lunch break. A female coworker carries a shiny purse and wears a fancy watch and was accessorized as such on that day. I noticed a tweaker-looking guy. I saw him in the reflection of a shop window. He appeared to be staring at my female coworker's purse. We walked about a half block and he was still following and looking at her purse. I picked a random shop and said pretty loudly, "hey, let's check this one out" and got us into the store pretty quickly. That got us off line and got me facing him without appearing confrontational. I now also had room to move without having to step into the street and I felt much better about reacting and -- if necessary -- getting my gun into play. He stared at us and then quickly crossed the street. He didn't bother with a crosswalk.
It's certainly possible he was just checking out my coworker's ass, but my gut said either a purse snatching or robbery. I suppose the biggest lesson here is that no, they don't just "come out of nowhere," which I suppose is the thing the color codes are supposed to help prevent. Using my environment (reflections) to be aware certainly helped me identify that. Having the mindset of, "yes, it is possible that bad things can happen in a 'nice' part of town, and yes, it's possible that bad things could even happen to me," as espoused by Cooper, @Tom_Givens, and a myriad of others, was definitely a factor in maintaining that alertness -- as was not walking around with my phone in my face. Doing a deliberate direction change, as taught by @jlw and others, helped me ascertain his intent and -- should it have become necessary -- would have helped me articulate why I took whatever defensive actions became necessary.