Script for row-banding alternating every nth rows

Question

I am looking for a google apps script that will alternate row banding color every nth rows (in my case it will be every 7), accounting for a one row header. I specifically want to use a script so that I can add and delete sets of 7 rows and automatically keep the banding on edit. Thanks! Richard

I managed to get alternating rows by myself but could not achieve multiples.