[crawfish]

This is the problem, most HTPC users use desktop full RGB and only switch to limited when playing media, so the kodi menu should be in full RGB and only the movie media should be limted. Currently its washed out so its taking the colour range from the setting in video which it shouldnt, it should be set to mirror the desktop colourspace.

Well, that's your problem. You need to commit to the optimal setup for video (0-255 card output, 16-235 for video players) instead of trying to have it both ways. No one wants to have to switch the color space on the TV when going between UI and playback. Alternatively, have Kodi output 0-255 and set your TV accordingly. That's the best compromise mode when you care about consistency between desktop and video. Of course, video must be expanded from 16-235 to 0-255, losing BTB and WTW in the process.

Really really surprised this hasn't been picked up on yet by anyone, its a fairly big deal really for videophiles.

Videophiles have the card output 0-255, the video players output 16-235, and set the TV for 16-235. They trade off desktop crush for passthrough video. This is the optimal setup for video. Kodi works correctly for them when its Limited Range option is selected, both UI and playback. In fact, it works better than WMC, which always renders its UI in 0-255, even when it plays video at 16-235.

BTW, it sounds like your TV is set to 0-255, which causes the Kodi UI to be washed out when its Limited Range option is enabled. However, if you're observing correct levels when playing video, the card must be outputting 0-255 for video, i.e. expanding the Video Levels Kodi is outputting to PC Levels. IIRC, this sort of thing can happen with Nvidia cards when you use the Nvidia Control Panel to change the Video dynamic range from "With the player" to RGB 0-255 and use DXVA2 in Kodi, which basically overrides Kodi's Limited Range option for playback. This would explain what you're seeing, and again, the solution is to configure the card to let the player decide, commit to 16-235 or 0-255 player output as previously described, and set your TV accordingly. Assuming your TV is capable, the optimal setup will show BTB (bars < 17) and WTW (bars > 234) in the AVS HD 709 Black and White Clipping patterns when you increase Brightness and decrease Contrast on the TV, respectively. The 0-255 approach OTOH will never show BTB or WTW, because they've been tossed out by the levels expansion from 16-235 to 0-255. That's one easy way to tell what's happening.