I have a 42" LG 42LK450 and I've noticed the same thing. What I've learned from searching around the internet is that somehow it isn't uncommon for different tvs to process different inputs slightly differently, even if they are the same type. and source. If you are using different sources, then they may be outputting the colors differently. If you are using different input types (cable, composite, component, vga, or hdmi) then they will almost always be slightly different. Another thing that I noticed with my LG tv is that some custom settings reset when you change inputs and must be set again for the new input. This may seem like a pain in the rear, but since each input is probably outputting things a little differently, it is often necessary to do a separate calibration for each input anyway.

If your tv has all the settings mine does (and I think it doe) then you can do a full ISF calibration to get your gray-scale completely gray and not tinted red at the dark end and blue at the bright end, then dial in your settings, but it requires equipment and needs to be done for each input.