title: plot axis labels with multiple colours
body: <p>I'm making plots like the one generated with the following code:</p>
  
  <pre><code>var1 &lt;- sort(runif(10, 0, 1), decreasing = TRUE)
  var2 &lt;- sort(runif(10, 0, 1))
  plot(var1, pch = 20, ylab = c("Var 1", "Var 2"))
  points(var2, pch = 20, col = "grey")
  </code></pre>
  
  <p>Is there a way, with just the R graphics package, to place a black circle before <code>Var 1</code> and a grey circle before <code>Var 2</code> in the y axis label, to avoid having to insert a legend? Or alternatively, a way to use different text colours (black for <code>Var 1</code> and grey for <code>Var 2</code>) in the y axis? I tried using <code>col.lab = c("black","grey")</code>, but it says <code>Error in plot.window(...) : graphical parameter "col.lab" has the wrong length</code>.</p>
  
  <p>Many thanks in advance,</p>
  
  <p>Márcia</p>