Fantastic post, but I'd like to add something.
Here in the Commonwealth, openly carrying a handgun is preemptively protected by our constitution. If you can legally own a handgun, you can legally OC it. I do this every single day-- I carry everywhere I legally can, the only exception being while I'm at work. Walmart, the mall, the movies, even the doctors-- my .45 sits Condition One at 3:30. And yet, I rarely get noticed, and even more rarely get bothered.
I've learned a lot about blending. Soemtimes, I stick out, but when your appearance fails to keep you grey, your attitude picks up the slack. I dress nicely, but not too nice; always wearing a fairly tight dress shirt, usually plaid patter, often wearing a fedora or a cabbie hat, with sensible jeans and steel-toe work boots (or Chucks, if I feel like it). I typically wear bright colors and am not afraid to look a little different. Why is this? Because the people that notice me are set at ease by my demeanor.
When someone does notice me, and when someone does notice my gun, they don't recoil. They don't gasp in shock and they don't call the police. This is because I carry myself as though I'm doing exactly what I'm supposed to be (and I am!). I walk very straight, I always wear a slight smile, I'm well-kempt and very polite, and I crack a joke at all the right times. You may want to call me fake, but being charismatic is a disguise in and of itself, no more or less than the hardhat and clipboard would be.
No, I don't get cops called on me. Instead, I get asked if I'm a cop. That's one of the most common questions, on the occasion that I'm disturbed. Most others genearlly either assume that I'm a cop off-duty or something (I've had a few people tell me they thought I was). The others typically just figure that my weapon is somehow linked to my occupation... I work in a factory.
Walking, speaking, and appearing like you're supposed to be where you are, doing what you are, will end all discussion about whether or not you're a shady fellow. If I wore a band tee and ripped up jeans, a backwards hat and had tattoos, and a bit of gut-pudge, I'd probably have a lot of problems carrying my firearm. But instead, I'm a 5'9" 120lb. guy (I'm light as a feather, but I don't look underweight; I appear well-built for being so thin) who dresses nice and is probably a plainclothes officer, and the people who talk to me walk out of the conversation with a smile on.
I would probably say that this is not so much being invisible, but moreso about misdirection. It's like comparing not being able to find something, to a slight-of-hand trick. Still, the effects are generally the same; people take little notice, and those who do are often either intimidated by your appearance (be it out of fear of the weapon, or out of feeling subconsciously inadequate because of demeanor/dress differences) or assume you are something far more normal than they would otherwise think without the disguise.
I play more on the assumption than I do on blending in. It's important to be able to adapt; if you're the grey man, and suddenly you're in the spotlight, then knowing a little bit of acting and misdirection could prevent a disaster. It's worked well for me so far.
Kudos on the post, OP. :3