[igraph] how to change attribute value

[Simone Gabbriellini]

Hello List,

I have two node attributes, name and colorname. I then have a list of values 
containing some of the nodes names. I would like to change the value of 
colorname for just the listed nodes.

I am using this but without success:

V(g)[name == listOfNodeNames]$colorname<-"violet"

thanks for the help,
Simone