I found this on Reddit, it's some basic information but this might help someone looking to buy a new TV.
Few pointers, 4K is expensive but not mainstream yet, HD works, if you're buying now, spent on the best HD panel you can get instead of buying a premium for 4K panels which will in future get cheaper and better.
Anyway, off to the copy pasta.
False: Plasmas have 3 bulbs behind the screen True: DLP TVs (no longer manufactured in mass if at all) have 3 bulbs behind the screen. True: Early Plasma TVs had problems with burn-in, but those have been largely eradicated.
True: Plasmas consume more power than LED-LCD TVs. They also produce more heat. True: The power consumption difference between LED and Plasma isn't very significant. A plasma tv (even at 60 inches) will use less power than a 2 slice toaster. In fact at 60" a plasma uses about half compared to a toaster. If you're energy contentious consider getting an LED, if you want a better picture look at a plasma.
True: Showroom floors at box stores don't demo tvs very well. TVs are often turned up as bright as they can go and the colors are shifted blue since blue looks bright. Plasmas don't respond to this as well as LEDs, so they look unimpressive. In a dark room they look much better with more neutral color rendition, better shadow details, much better contrast, and more color saturation available. Also please pay attention to the content on the tvs. Usually they're showing some sort of advertising loop in box stores and showing real movies in electronics stores. Do not buy a tv until you see skintone on it. Compare skintones between the tvs you're thinking about buying. Do they look orange? Do they look plasticy? The vast majority of what you watch on a tv will be people, and it's important to see how people look, not motion graphics.
False: 720p upconverted will look better than 720p. When you up or down convert you make artifacts. When you convert up then convert down you make artifacts, then you make more artifacts based on those artifacts. If this was the way to go everything would be converted to 4k or more at studios and tv stations then it would be converted down. True: Avoiding converting the resolution makes for the best picture. If you have a 4k display all 480i/p, 720p, and 1080i/p sources must be unconverted since the panel is 4k. The 4k tv will still look great, so don't let this conversion factor into a 4k decision.
Ambiguious: The salesman was kind-of right when he said 4k can display more colors than plasma or lcd, but he didn't know what he was saying. There's a tl;dr in italics.
Digital images always have a "Color Space." With digital images colors are expressed numbers, and we can decide what those numbers mean. Some color spaces are limited, so when you get a brand with a very bold color you may not be able to produce it in SD or HD, but it may be possible in UHD.
To be clear, 4k is the fidelity, or the number of pixels. Chances are you're looking at a UHD tv (3840x2160) on the showroom floor, not a 4k (4096x2160) tv. The color he mentions comes from the color space used by HD and UHD. You're likely to see UHD used interchangeably with 4k in stores and online. While it's incorrect, the world seems to be embracing it as correct. I'm just a stickler.
HD used the Rec. 709 color space. UHD uses the Rec. 2020 color space. As you can see here [ , Rec. 2020 (UHD) can display far more colors than Rec. 709 (HD).
What I believe the salesman (should have) meant when he said 4k can show more colors than lcd or plasma is that until you get to the top end LED-LCD and plasma struggle to show all of HD's colors. They usually crank the saturation up to make you think they have a lot of color, but lower end tvs rarely show off of HD. Low end UHD tvs don't exist yet, so they're going to be better about the colors they can reproduce.