title: Overriding default colours in a ggplot diagram
body: <p>I'm fairly new to R and am trying to change the colours of my generated diagram.
  <a href="https://i.stack.imgur.com/8lpfz.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8lpfz.jpg" alt="enter image description here"></a></p>
  
  <pre><code> p = ggplot(plasma1, aes(x=Day, y=Control, colour=Supp))
   + theme(panel.background = element_rect(fill='white', colour='black'))
   + geom_point(size=2, shape=21) 
   + geom_errorbar(aes(ymin=Control-SEMcontrol, ymax=Control+SEMcontrol), width=1)
  
   p + theme(panel.grid.major = element_blank(), panel.grid.minor = element_blank()) 
   + xlab("X") + ylab("Y") + geom_line(linetype="dashed")
  </code></pre>
  
  <p>I've looked at themes() but I can only seem to change the grid lines and not the trend line. (Ideally I would like to change red &amp; blue to red &amp; black</p>