It is from some plastic film mate, yes. I did this on my Corrado, and its fairly easy, just a little time consuming.
You can remove the coloured film and replace with a coloured LED, or you can just replace the film with a different colour. You can get it from hoobycraft and the like.
Be sure to mark where the needle sits before you reomve it from the clocks though, otherwise it may over/under read. If its like my Corrado then although the needle sits of its rest, this isnt the furthest it wil travel. You may need to lift the needle over the rest, and see if it travle a bit further. this is where you need the mark.