[R] Color index in image function

[FMH]

Dear All,

I was looking for the color index in image function, such as from topo.colors(n) and etc. but still never found it. For instance, from the help menu.


###########################################
# Volcano data visualized as matrix. Need to transpose and flip
# matrix horizontally.
image(t(volcano)[ncol(volcano):1,])

# A prettier display of the volcano
x <- 10*(1:nrow(volcano))
y <- 10*(1:ncol(volcano))
image(x, y, volcano, col = terrain.colors(100), axes = FALSE)
contour(x, y, volcano, levels = seq(90, 200, by = 5),
        add = TRUE, col = "peru")
axis(1, at = seq(100, 800, by = 100))
axis(2, at = seq(100, 600, by = 100))
box()
title(main = "Maunga Whau Volcano", font.main = 4)
#########################################

From the script above, it yields a beautiful  image of volcano with variety of colors but i have to list down the color index that could show the meaning of each color in my thesis. 

Could someone please help me to extract this color index?

Thank you
Fir