I changed my ED cluster to red. However, it could only be changed to red because the lights are actually clear, and comes through orange because of the plastic. So had to be red, otherwise it'd come out brown
Not sure how AU's are, as far as that is concerned... and also not sure if cluster is similiar in any way to ED (as far as fitting etc). But if it is, the instrument cluster should unscrew, and slide out. Then, at the back there are little plastic plugs/screws that twist out... take out the appropriate plug/screws and u'll find it has a globe on it... slap a colored condom on it, and away you go.
No idea if AU is like that, but ED is.