ggnetwork::geom_nodes() requires more colors than there are nodes

Question

Load ggnetwork, network, sna, igraph, and ggplot:

library(igraph)

library(network)

library(sna)

library(ggnetwork)

library(ggplot2)

Create an igraph object with five vertices and two edges:

test <- structure(list(5, TRUE, c(0, 3), c(4, 1), c(0, 1),
                 c(1, 0), c(0, 1, 1, 1, 2, 2),
                 c(0, 0, 1, 1, 1, 2), 
                 list(c(1, 0, 1), 
                 structure(list(),
                .Names = character(0)),
                list(name = c("3", "6", "7", "2", "1")),
                list(weight = c(3.30310760667904, 3.55724789915966))), environment),  
                class = "igraph")

Check the number of nodes and edges:

igraph::ecount(test)
[1] 2

igraph::vcount(test)
[1] 5

The following code works (it should not work, notice that the number of color values in geom_nodes() is wrong, there should be five values, but 7 are given):

ggplot(test,aes(x = x, y = y, xend = xend, yend = yend)) + 
       geom_edges(arrow = arrow(), color = 'black') + 
       geom_nodes(size =10, aes(color=1:7/(7))) + 
       scale_color_gradient(low = "green", high = "red")

If if the correct number of values for geom_nodes(aes(color= )) is used instead, an error is generated:

ggplot(test, aes(x = x, y = y, xend = xend, yend = yend)) +
      geom_edges(arrow = arrow(), color ='black') + 
      geom_nodes(size =10, aes(color=1:5/(5))) + 
      scale_color_gradient(low = "green", high = "red")

Error: Aesthetics must be either length 1 or the same as the data (7): colour

Notice that geom_nodes seems to require that |color| = |nodes| + |edges|, why is this? Is there a way around this? If there are 7 colors passed, how does it decide which 5 to use for the node colors?