What does it do?
For broad-band Internet the HDR (UHD color) is always on. Some models of Samsung UHD tv's came with not quite the full convention for HDR. So was called UHD color. Using a HDR color test pattern found on You Tube shows you don't quite get the full color range for HDR.
It should be turned "on" for HDMI ports using 4K compatible HDMI cables. If you read your Samsung manual it explains that when using Cable (or Satellite) channels having it "on" might cause stuttering. I have never seen the problem on my 120 Hz Samsung 3D UHD television, so I leave the ports "on" UHD color.
I should have added that this setting needs to made for each port used for UHD color. Use it for; 4K dvd players, 4k X-boxes, or 4K cable / Satellite. 4K gaming might have "stuttering" since require more motion.