title: Highlight point in ggplot2
body: <p>I would like to highlight a single point (always the last) in ggplot2. </p>
  
  <p>I have got most of the way there with the following, however there are a few issues. First, the <code>color = 'red'</code> part of the code does not appear to be working, as the point is pink.  Next, the point <code>red</code> is added to the legend. </p>
  
  <pre><code>testDF &lt;- data.frame('A' = rnorm(547), 'B' = rnorm(547), 
                   'date' = seq(as.Date("2012-01-01"), as.Date("2013-06-30"), by = 'day'))
  
  testDF$qtrYr &lt;- factor(paste0('q', 
                              as.POSIXlt(testDF$date)$mon %/% 3 + 1, 
                              '-', 
                              as.POSIXlt(testDF$date)$year + 1900
                              ), 
                       levels = c('q1-2012', 'q2-2012', 'q3-2012', 'q4-2012', 'q1-2013', 'q2-2013'),
                       ordered = TRUE)
  gp_XY &lt;- ggplot() +
                  geom_point(data = subset(testDF, testDF$date &gt; as.Date("2012-04-01")),  
                             aes(x = A, y = 100 * (A - B), color = qtrYr), pch = 1) + 
                      labs(y = NULL, x = NULL) + 
                  geom_smooth(data = subset(testDF, testDF$date &gt; as.Date("2012-05-01")),  
                              aes(x = A, y = 100 * (A - B), color = qtrYr), 
                              method = 'lm', se = F, size = 1.25) + 
                  geom_point(data = tail(testDF, 1), 
                             aes(x = A, y = 100 * (A - B), color = 'red'), pch = 19, size = 2)  
  </code></pre>