[Milhouse]

It started with Build #1005 (Oct 5th). 

Then this is almost certainly down to the fixed-function pipeline change. Please open a ticket on trac.kodi.tv as that's how the developer likes to receive his bug reports.

I was referring to xrandr's "Broadcast RGB" flag.

I think you're referring to the passthrough full/limited patch which was dropped in #1216 and applied only to Intel GPUs. This kernel patch was removed because, well, people complained the display was too dark (and nobody commented positively/negatively following its removal so either it had no effect, or everyone is too polite to say anything).