According to the MythTV How-To docs, the F key is used to "rotate between the various Picture Adjustments (Colour, Hue, etc.)" when watching TV or a recording. For some reason this doesn't work on my frontend. Oddly, the G key will cycle through these adjustments for the recording settings, but I'd prefer not to mess with those since they seem okay. I'm using R5A26 on a Via EPIA M1000 with the built in S-Video out. The picture isn't that bad, I'd just like to see if I can tweak it a bit. Is there another way to adjust the picture on playback?

Under the Setup menus hunt around for the "use Xv picture controls" check box and enable that. I think it's under TV -> playback, but it might be TV -> general.