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I apologize for past mis-information. I am researching heavily and correcting as I go.

To Enable true 4:4:4 Chroma / Color Sampling at, follow the steps below. My graphics card only supports 30hz at 4k. The in-TV menu says explicitly that enabling UHC color is for “4:4:4 at 50p & 60p”

Also, the user manual explicitly states 4:4:4 4k at 60 hz will work on page 217:

This is a long thread on the nVidia forum that indicates some troubles with Samsung sets. It appears that several sets are receiving firmware updates that are fixing the issue, this enabling 4k 4:4:4 at 60hz:
https://forums.geforce.com/default/topic/776523/geforce-900-series/gtx-980-can-t-get-4k-at-60p-on-samsung-tv-/5/

So far, the rough consensus is that 4k 4:4:4 at 60hz is still not working for this exact set. 🙁 Below are the steps for enabling 4:4:4 color:

1. Use the first HDMI port – “HDMI 1” is the name of the top most “first” port. Don’t confuse this with version 1 or 2 of the HDMI technology.
2. Update the latest firmware. If your TV is connected to the internet, the option to update the firmware will eventually light up, though it will appear grayed out initially. Give it a few minutes (like 30). I’m on version 1052 after the update.
3. Enable UHC Color from the TV menu under “Picture Options” on that first HDMI port – remove any cables plugged in before enabling.
4. Rename the 1st HDMI Port to “PC” from the source menu by tapping and holding the remote control direction pad button on the HDMI1 source. When you let go, a sub menu will appear to rename the source. Select PC.

4:4:4 will not work until you rename the source to PC (what an awful UI requirement, but at least it works). You will also experience really bad mouse input lag until you rename the source to PC.

If you have a Kepler nVidia video card (which is not new anymore), then it will suport 4k 4:4:4 at 30 hz. I run a GTX 680 and it’s great. This is just fine (no flicker) for windows usage, but you will want 60hz for gaming. I hope a firmware update enables this.