I see. Then what you could do is adding a vertex attribute, named (say) "Opinion", and then update that based on the network structure, e.g. (in R):
library(igraph)
set.seed(42)
net <- erdos.renyi.game(40, 2/40)
V(net)$Opinion <- sample(1:2, vcount(net), replace=TRUE)
coords <- layout.auto(net)
colbar <- c("orange", "cyan")
layout(rbind(1:2))
par(mar=c(0,0,0,0))
plot(net, vertex.color=colbar[V(net)$Opinion], layout=coords)
## Set the opinion based on the neighbors
V(net)$Opinion <- sapply(V(net), function(x) {
round(mean(V(net)$Opinion[neighbors(net,x)])))
plot(net, vertex.color=colbar[V(net)$Opinion], layout=coords)