[PatK]

Either you haven't made it abundantly clear with some sort of dotted line and a proper colour test target, or I've got a screwed up monitor and TV set-up. If there is colour variations, then you might investigate 'limited colour range settings' in system. Video levels and color space (wiki) To answer your question of why there should be any variation in colour saturation might have more to do with the driver, than Kodi. Kodi just throws up the data at the graphic engine, and it's that part of your system that takes over and turns it into an HDMI digital signal. Try software rendering and see if that changes anything for you?

[Edit} I'm moving this off to video support.