Assigning materials for render in Grasshopper

Hi everybody,

I designed some objects like this one :

https://www.flickr.com/photos/fdecomite/23725712760

but for rendering, I didn't find  a simpler way to assign colors to pipes than to define them in Flamingo. Is there a way to define rendering materials/colors to objects in Grashopper ?

(my method is unappliable when I generate dozens of pipes...)

Thanks in advance !

Francesco De Comité