Ah... discovered that colours in the colour window can be changed. I located the green colour (default for audio instruments) and changed it to a nicer blue colour, which has automatically changed all of the audio instrument channel colours. So now if I record some midi the sequences will be coloured with the new 'blue' rather than the old green.
This is good. But I was hoping that anything on the screen using that green would also change to blue, ie. the cycle bar, but that hasn't happened.