title: ggplot Colour-labelling
body: <p>Simple question: I have the dataframe, <code>df</code>, below, I can scatter-plot and colour-label based on the <code>label</code> column of <code>df</code>:</p>
  
  <pre><code>if(!require("ggplot2")) { install.packages("ggplot2");  require("ggplot2") }
  set.seed(1)
  df &lt;- data.frame(a= rnorm(30, mean=1, sd=1),
                  b= rnorm(30, mean=5, sd =2),
                  labels= sample(c(1,2,3), 30, replace=TRUE ))
  ggplot(data= df, aes(x=a, y=b)) +  
  geom_point(data= df, colour=df$labels, shape=1)
  </code></pre>
  
  <p>However, I do not know how I can specify the actual colours (e.g. pink, magenta, cyan) for labelling.</p>
  
  <p>I tried adding the code below to the ggplot but it does not work:</p>
  
  <pre><code>scale_colour_manual( name = "Name", values = c(1 = "pink", 
                                                 2 = "magenta",
                                                 3 = "cyan"))  
  </code></pre>
  
  <p>How can I specify the colour in this context?</p>