You talk about ratings, but use a designation "3+" which is not an official NIJ rating and means different things to different manufacturers. What THREATS are you hoping to defeat? For instance, M855 green tip is NOT stopped by all 3+ plates. I am not aware of any rifle plate on the market that will defeat M855 and weighs under 4 lbs. To stop M855, you have to get a "
3++" or "
3+ Special Threat" or some other funky name - everyone has a different designation. For that type of rating though, the lightest I've seen is around 4.6 pounds from DFNDR, or 4.8 lbs from Armour-Wear for literally 60% cheaper. Velocity has a plate (7.62x39 (API-BZ) Multi-Hit Stand-Alone Rifle Plate) that weighs the same, but is only 0.5" thick instead of 1.1" thick so they'll conceal much better.
The white carrier will likely have to be custom manufactured. I've never seen one regularly stocked by any of the common mfgrs. If you're going to get thin plates like the Velocity ones I mentioned above, TTG has a nice low-viz carrier which is perfect for concealed wear. They might make one for you in white.
http://www.trentontactical.com/ttg-wag-lo-pro/
Finally, if you're standing around on guard duty all day, I suspect you will stop wearing rifle plates after very long and just stick with your soft armor.