Easy!

I briefly wrote how I did it in the post where I introduced car (As I had done this mod just before I joined Antrx), this thread was relevant just to the Indiglos but the guages fit in too, so.

Look through the pics as you read and you'll probably understand easily
http://rgrant.communis.com.au/Stuff/CarDashMod/ <-- First photos of when I made guages Red
http://rgrant.communis.com.au/Stuff/Dashmod%20Blue%20Experiment/ <-- More recent experiment with Blue modelling paint, worked very well
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What you need:- A little jar of modelling paint of desired colour (Flat, common colours like Red and Blue are best, nothing too light or dark). Available from modelling type places, only a few dollars, and will be MORE than enough to do the lot.
- Small paintbrush to apply paint. Available as above if you need one, or perhaps just improvise if your only doing this once.
- Some mildly-rough sandpaper

Something a few hundred grit should work nicely.
Howto:1 - Take the guage cluster out. I've posted how to get to it somewhere else, I'll post a link when I find it later. I'm presuming you are getting that Corsair one calteoh? Just take off the clear cover and black part with the circles (Clips on top and bottom), pop off the needles (Screwdriver underneath and twist if theyre reluctant), and then undo the two screws on each guage face and lift it off. Be careful, these screws are easy to loose and are delicate, so be gentle with them or you might bugger the heads up.
2 - See DashMod01.jpg .. Remove the guage faces. Flip it over. The white/green stuff, with dots in some areas, is what makes the light green. I presume the diffrences in area (With/without dots etc) help even the light. We can't do this when we mod them so the guages may be lit unevenly, but who cares
3 - See DashMod02.jpg + DashMod04.jpg .. First we need to remove the green stuff. If you want to leave the tacho redline, indicator arrows etc as-is, cover them with masking tape first!! When ready, sandpaper off the green stuff.
4 - See DashMod03.jpg + DashMod05.jpg .. Paint on the modelling paint! Also leave any masking tape on for this step. If you are doing a large area like the indicator arrows, try and keep the paint as even as possible otherwise it will appear very 'blotchy' (Can see un-evenness in the paint when lit). However for numbers and such you can get away with it.
5 - See DashMod10.jpg to DashMod12.jpg .. Leave paint to dry (Should be fine to fit guage faces back on after around 5-10 minutes) and then check against a light and re-install. (If your not going to do led needle mod too

).
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Very easy, and should take under an hour to do

Note that when reinstalling the needles, the fuel and temp ones fit onto half-circle things so they don't need to be adjusted. Speedo, Tacho (and Oil Guage needle if you have it) will go on anywhere, but can point to the wrong position on the guages. To fix this, understand that there is a "Low limit" where the needle moves to and stops when you let it go. There is also the upper limit, where the needle will stop when you push it as far as it will comfortably allow.
What I do is simply put the needle on. If it points to anywhere below zero whilst at its Lower limit, I push it to the Upper limit and then keep forcing it slightly. Then if the
Lower limit is above 0, I carefully keep forcing it past the lower limit until it points to the right spot (0).
It might be a little tricky to understand but have a play with the guages and you'll understand. I did the Tacho first as I would rather have an inaccurate Tacho than an inaccurate Speedo, for obvious reasons. My guages still work perfectly and are accurate after being this, but I would advice caution - don't force the needle around over and over and over again because we don't want to break them. Try and keep it as accurate as you can to keep the need for adjustment to a minimum.