I have made a number of these in the past and use see through green and blue combo for more realism:
don't forget to add Microsol Crystal Clear or any other white glue to add the lens and make it look reflective. You can also add wires by drilling the side of the plastic piece and attaching wires that would go into the dash.
Also you can add decals to represent various brand names of the Engine Managament or Turbo Timer units.
Use the same tehnique to make Radar Detectors, etc.