[noggin]

I've noticed something today.
Playing 4k Movies on Kodi makes the colours washed out. Playing a 1080p movie and the colours look good.
Playing 4k Movies on SPMC and they look fine.

What's going on?

Is this to do with the colour space issue being discussed here? 

Potentially - the OP doesn't say whether the 4K content is HDR - but I'm guessing it is, though they don't say what their display is capable of and how their Kodi/SPMC and Nvidia Shield TV are configured, so it's really difficult to tell anything...