Coloring service area using QGIS and GRASS tool v.net.alloc

Question

I try to work with v.net.alloc to find some service area for my problem in QGIS 2.18.13. That algorithm work nice create categories from my roads for any hotspot like this :

and if use style categories then I have a simple coloring road map for any hotspot.

My question is how to coloring all service area and not only the service road like this example :

I need with the some method to coloring all area from service area using v.net.alloc.

any idea ?