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.

 

 

 

  

Further examples

 

 

Thanks to Duncan Brinsmead for his original fluidTexture2DShape texture.