Grey material from current renderer......

Hay fellow scripter i little know how to make grey material but I want to extend it a little further, that is create a grey material from current renderer type, so material type will follow current renderer like

- if the current renderer is vray the material class type of grey materal is vrayMtl
- if the current renderer is mental_ray the material class type of grey materal is Arch___Design__mi and so on...

I already try this if current.renderer mental_ray then grey material .....but failed....I know im not scripter man.

thank