Ah I get it now. So with adapted lenses the histogram is more true, as in the same as what is shown in playback mode. But with native lenses it changes to yellow when the exposure isn't correct and displays the graph for the correct exposure, not changing as the aperture is changed on the camera.
Shame. So it's not possible to have the histogram show up in the preview?
It changes to yellow for adapted lenses as well, it changes colour when under or over exposure is dialed in via the rear dial. The only difference when using native lenses is that a further display is shown for the f stop and speed. Adjustment of the histogram to the right or left by exposure compensation is the same for both native and adapted lenses.
Thanks Barrie, I think I understand now. I've been using manual mode exclusively up until now as I understand the implications of aperture and shutter speed in relation to the shot I will end up with and the shot I want.
The only change I have seen in the histogram is white at correct exposure, or yellow for over/under exposure. The actual graph never changes in manual mode.
So to have the histogram display what I want it to (an appropriate graph for the current settings) I need to use either aperture or shutter priority and use exposure compensation to alter the non priority parameter. Is that correct?