The modern tactical vest, first popularized by 5.11 Tactical, is a very well thought out, functional item. I first saw them used in the field in late 2002/early 2003 by spec-ops troops working EP (executive protection) details in Afghanistan. I personally own an Orvis Travel Vest (the granddaddy of all modern tactical vests), a Banana Republic vest from the 1980s (back when they actually made clothing suitable for wearing into banana republics), and a new Woolrich Elite vest very similar to the ubiquitous 5.11 vest.
If you attend an IDPA match, you'll see that the great majority of competitors wear 5.11 tactical vests as their covering garment during the competition.
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That is perfectly fine. What I want everyone to realize, however, is that these kinds of tactical vests are the fashion equivalent of the unmarked cop car when it comes to real world carry. I highly caution against wearing them as a covering garment for your legally concealed handgun when out on the street.
The tactical vest is as much a victim of its own success as anything else, but the fact of the matter is, when I see anyone wearing one, no matter where I am, I immediately assume they're armed. There is a reason why, locally, we refer to the 5.11-type tactical vests as the Shoot-Me-First vests or the IDPA Cape. They have become synonymous with concealed carry, and a lot of the bad guys know this as well.
Now, if your intention is to let everyone around you know you are carrying a gun, without the burden of true open carry, that's fine. Wearing 5.11 apparel, you can be immediately recognized by those in the know as a member of the in-crowd, much like driving a Prius is a symbol to the "I care more about the Earth than you" liberal crowd. If, on the other hand, you are concealing your pistol because you want to pass unnoticed amongst the general populace, the tactical vest is not for you.
If you just must wear one on the street, get it in black, or green; any color other than "contractor" khaki. Your concealing garment should help protect you, not make you a bigger target.