I've discovered there are some formatting options on the GNU Plot graph after it has been generated through octave. If you press 'm' it's then possible to right click and get a menu with choices to format the plot (line styles/colour/background/print). However, for me it crashes a lot and changing the values doesn't seem to have much effect.
There is some other functionality by using these key presses..
- m - allow menu on right-click
- a - zoom to full window
- p - previous zoom level
- r - overlay ruler
- g - overlay grid
- b - toggle border
- 1 - toggle output reading format
- 5 - display radius measure tool (when ruler is displayed)
- 7 - format aspect ratio (useful to get square plots to not distort scale)
These are just the ones I've found by randomly testing the keyboard (!), so this is hardly exhaustive. But hope that helps.