R networkD3 sankey - change the colors for all links to blue

Question

Here is example code that I use to make a Sankey chart using networkD3::sankeyNetwork()

library("networkD3")

a <- read.csv(header = TRUE, text = "
date,Data Center,Customer,companyID,source,target,value 
6/1/2021,dcA,customer1,companyID1,open_list_view_1,open_card_2,1 
6/1/2021,dcA,customer1,companyID1,open_card_2,edit_card_3,1
6/1/2021,dcA,customer1,companyID1,edit_card_3,save_card_4,1 
6/1/2021,dcA,customer1,companyID1,save_card_4,back_to_card_list_5,2 
6/1/2021,dcA,customer1,companyID1,back_to_card_list_5,show_more_6,1
6/1/2021,dcA,customer1,companyID1,show_more_6,view_introduction_7,1
6/1/2021,dcA,customer1,companyID1,view_introduction_7,scroll_down_8,2
6/2/2021,dcA,customer2,companyID2,open_list_view_1,open_card_2,3
6/2/2021,dcA,customer2,companyID2,open_card_2,edit_card_3,1
6/2/2021,dcA,customer2,companyID2,edit_card_3,save_card_4,4
6/2/2021,dcA,customer2,companyID2,save_card_4,back_to_card_list_5,2 
6/2/2021,dcA,customer2,companyID2,back_to_card_list_5,show_more_6,1
6/2/2021,dcA,customer2,companyID2,show_more_6,view_introduction_7,1
6/2/2021,dcA,customer2,companyID2,view_introduction_7,scroll_down_8,5
")

node_names <- unique(c(as.character(a$source), as.character(a$target)))
nodes <- data.frame(name = node_names)
links <- data.frame(source = match(a$source, node_names) - 1,
                    target = match(a$target, node_names) - 1,
                    value = a$value)

sankeyNetwork(Links = links, Nodes = nodes, Source = "source",
              Target = "target", Value = "value", NodeID = "name",
              sinksRight = FALSE)

I want to change the color for all links to blue. I think the argument 'linkgroups' might help.