The back lighting on my dials (From memory.) had four T10 capless white filament bulbs with a green rubber sheath over the actual bulb that gave the hue..! Mine is a 95 plate tintop, so may be different to the later shape..
I replaced mine with red led's at night the yellow needles have a VW glow... (Well... Ish!!??)
The plasma dials can also be dimmed to taste...
...& ironically, with a switch changed to green.!
