My idea was since the light behind the gauges is a regular bulb and not a monochromatic LED, transparent tape or paper will produce the color you want.
For instance, the bulb they have emits light across the spectrum, so if you put blue transparent paper in front of it, blue light comes through. If you put a red monochromatic LED in, it only has light in the red wavelengths of the spectrum, so if you put blue paper in front of a red LED, you really won't see much of anything.
Instead of replacing the bulbs with LEDs, wet sand off the green transparent film off of the gauge (you can leave the red film by the km/h part for a cool look), and put on a similar kind of blue film where the green film was for the MPH. This way, it should still be bright because basically your doing the same thing that ford did just using blue instead of green.
I'm not talking about electrical tape, I'm talking about transparency film or sticky transparancy film would be easiest. c.ohamara found some on ebay and there is a link to it a page or two back in this thread check it out and tell me if it works. Its extremely cheap and sounds pretty easy.