title: ggplot red-white gradient appears orange
body: <p>I've created a heat map in ggplot and I'm using a default red to white <code>scale_fill_gradient</code>. When I plot the gradient however, it appears to have an orange tint. I was wondering if there was a way to edit how <code>ggplot</code> calculates the gradient so that I get pink intermediates so that it matches the other figures I'm making. Related to this graph, though I can post separately, I want to make my NA values have a striped pattern (rather than grey fill). I haven't found a way to do that in <code>ggplot</code>. </p>
  
  <pre><code>    p &lt;- ggplot(heat.data, aes(x = MutResFac, y = mutAA, fill = disruption)) +
              geom_tile(color="grey50") +
              scale_fill_gradient(name = "Disruption", limits = c(0,3),
                                   labels = c("WT-like", "Mild", "Moderate", "Severe"),
                                   low = "#FFFFFF", high = "#FF0000",
                                   guide = "legend") +
              theme(axis.text.x = element_text(size = 25, hjust = 1), 
                    text = element_text(size = 25), 
                    plot.title = element_text(hjust = 0.5)) + 
              coord_fixed() +
              labs(x = "Position", y = "Mutant Amino Acid") +
              ggtitle(title) + 
              scale_x_discrete(labels = wildTypeSeqLabels) 
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/SyP16.png" alt="A example plot of the data"></p>