HDMI UHD color mode question

[Nysta]

I recently bought a 2018 q8fn 55" tv and from what I understand is that the HDMI UHD color mode is for hdr/4k capable devices plugged into the HDMI ports and need to be enabled individually on each port.

My question is if I leave it enabled on all ports all the time. Will there be any negative effects to non hdr/4k capable devices? And if  there isn't any problem, then why is it disabled by default or even have an option to disable it in the first place? Why not just set it and forget it?

[Madasahat]

Turn them all on and if you find a device does not show and has a black screen then change it. 

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[ienichols]

Samsung UE40MU6470U TV:

With my Denon AVR-X3300W, enabling HDMI UHD Color on the TV input from the AVR mutes the AVR sound received over HDMI from my Humax HDR-Fox-T2.  Adding a parallel optical audio cable from the HDR to the AVR or turning off UHD Color will solve the problem.  A Bluray input to the AVR was not similarly affected...