I tried to change the colour of the bulbs on my Primera. As standard, they are sort of a light blue. The needles however lights up red. When i removed the bulbs from the back of the clocks, i noticed that the bulbs had a rubber hood, which was coloured blue to give the effect. There are also two different sizes of bulbs which illuminate the clocks and i believe that they're not all 12 volts, so its very hard to find replacement coloured bulbs. The only thing you can do is, like you say, removed the rubber hood and paint the bulb with blue tint, or whatever colour turns you on
The only problem is, that by changing the colour of the bulbs, you also change the colour of the needle, so beware!
What i wanna know is, has anyone dismantled the clocks to colour code the black surround that seperates each dial. I'd like to do mine in silver to match the rest of the dash.