title: How to change the title of Y axis in ggplot2?
body: <p>I have data like this:</p>
  
  <pre><code>      test_data &lt;- data.frame(
        var0 = 100 + c(0, cumsum(runif(49, -20, 20))),
        var1 = 150 + c(0, cumsum(runif(49, -10, 10))),
        date = seq.Date(as.Date("2002-01-01"), by="1 month", length.out=100))
  </code></pre>
  
  <p>To plot both time series var0 and var1 on the same graph, with date on the x-axis, using ggplot2</p>
  
  <pre><code>             ggplot(test_data, aes(date)) + 
               geom_line(aes(y = var0, colour = "var0")) + 
               geom_line(aes(y = var1, colour = "var1"))
  </code></pre>
  
  <p>This will work fine and plot two time series in different colors but the title of Y axis and the legend will be"var0".</p>
  
  <ul>
  <li>How to change the title of Y axis and the legend to,for example,variable , value</li>
  <li>how to change the colors of both var0 and var1 lines</li>
  </ul>
  
  <p>Thanks</p>