title: Symbol fill color in lattice using auto.key
body: <p>I'm making a plot using <code>xyplot</code> in <code>lattice</code> (R 15.2, lattice 0.20-13) in which I have several groups that I would like to distinguish by the shape of the marker. I need to use a downward facing triangle which is only available as a hollow symbol (<code>pch=25</code>) unlike up triangle which is available as a filled (<code>pch=17</code>) or hollow (<code>pch=24</code>) symbol. I can specify both the outline color and the fill color for these symbols in <code>par.settings(superpose.line())</code>, but when I plot an <code>auto.key</code>, there is no fill. Is there some way to get the <code>auto.key</code> to be consistent with the plot symbols? </p>
  
  <p>This is an example of what I'm describing: </p>
  
  <pre><code>data &lt;- data.frame(x_var = rep(1:10, 2), y_var = rnorm(20), group=rep(c(1,2),each=10))
  
  xyplot(y_var ~ x_var, groups=group, data=data,
         par.settings=list(superpose.symbol=list(col=c("red", "blue"), fill=c("red", "blue"), pch=c(24, 25), cex=2)),
         auto.key=list(space="right"))
  </code></pre>