Have a look at this thread:
We have been working on the thermal governor for the vero4k and this should prevent crashes caused by overheating when the device is used in hot locations with heavy cpu use.
My own vero4k on my main TV was freezing in the same way you describe - a solid colour when left “idle”, usually overnight.
Mine is inside a TV cabinet that gets quite warm due to other equipment and the device has many background services installed as well, which was sometimes pushing the CPU temperature to the point of instability.
Contrary to intuition Kodi uses a lot more CPU when left “idle” especially on the home screen or a screen with auto-scrolling text than it does when actually playing video, which is why the crash won’t typically occur when it is being used to watch video.
I’ve had no crashes at all since updating to the test kernel. You can try the test kernel early as described in that thread, or wait for the next monthly update due sometime in the next week or so which will include the fix.