LEDs my arse. LEDs would not need the power supply to output voltages like 19, 22 and 28.5V.
The disco dash is one big fluorescent display with lots of small elements. It uses a two dark green translucent sheets to give it the colour (maybe three if you count the tripmeter). It seems almost like a welding tint when you hold it up to the light.
With precise cutting you could make the display almost any colour you want, limited by the translucent sheet you could buy. Precision is the key.
I have toyed with the idea of changing some colours in the display. For example, it would be nice to have the upper bars of the temp and voltmeter displays in bright yellow, orange or red, making abnormal conditions much more obvious.
If you want to experiment then you might be able to find a dead dash display at a Z wrecker for pretty much no cost. As long as it is complete then you are set.
It is worthwhile just to remove your existing dash display and dismantle it back to the green sheets.
Over time, the plastics inside release some plasticiser which fogs the display a bit. A good wipe of the fluoro display and some Plexus on the green sheets and the transparent outer cover will restore the display to new-like crispness. Just be careful with dust as static will build up when you wipe.
There are three digital dash styles.
They are all of the same internal design, but they look slightly different.
The 85-86 made the RPM band the same distance from 1000-2000 as it is from 5000-6000. 1984 had a wider distance between 1000-2000 than it did from 5000-6000 rpms.
87-89 dropped the oil and volt meters and they were relocated to the center pods (also dropped G meter and compass) in analog pods that were lit to resemble the digital gauges.
Yes. They all still used the same basic LEDs for the speedometer and tach.