You are right its simple. LOL. There are many ways of going at it. My first thought would be is to create 3 custom model . First one of the whole star. The second and third I would copy it then remove the center on one and the outer on the other. Just be sure you use the same channel numbers for each node. Now for the tricky part. The render order. What you do is place them in order of rendering so the full model is rendered first and the small sections second so they will over write. Saying if you make the whole thing blue and then make the center twinkle. It will come out just what you want.
