A better way to create a bubble shader is to use Thin Film.
This tutorial shows how to shade the swirling rainbow color effect on a soap bubble. It can be achieved using a fluidTexture2DShape. This scene file consists of a fluidTexture2DShape that is connected to the Specular Color of a Standard Surface shader.
|The scene can be downloaded here.|
fluidTexture2DShape connected to Specular Color
You must play through the animation time slider in order to see the fluidTexture2D effect.
Thanks to Duncan Brinsmead for his original fluidTexture2DShape texture.