title: Order sequential colour palette from dark to light in ggplot
body: <p>I am having difficulty ordering my customised sequential colour palette so the highest values in my plot are darkest and the lowest values are lightest.</p>
  
  <p>My data is below.</p>
  
  <pre><code>dput(preseason18)
  #&gt; Error in dput(preseason18): object 'preseason18' not found
  structure(list(Week.Number = structure(1:16, .Label = c("1", 
  "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", 
  "14", "15", "16"), class = "factor"), Distance.18 = c(5331.83038, 
  14084.08602, 12219.423585, 14406.407445, 5032.74848, 10820.094835, 
  16935.546075, 15387.590625, 16195.21247, 20012.09881, 14057.385255, 
  5127.14891, 16241.98523, 12793.21837, 10526.785375, 6014.43878
  ), HIR.18 = c(1098.56001, 4093.010015, 4372.84498, 4074.22002, 
  709.70499, 2460.04999, 5037.77501, 5521.029965, 5463.410025, 
  6761.34502, 3953.20997, 1189.89, 3663.69006, 2333.005005, 2289.38001, 
  1069.740005), V6.18 = c(0, 40.77, 63.505, 112.63, 52.395, 56.795, 
  211.115, 75.52, 215.059995, 121.725, 57.64, 15.35, 140.34, 15.615, 
  85.66, 31.815)), .Names = c("Week.Number", "Distance.18", "HIR.18", 
  "V6.18"), row.names = c(NA, -16L), class = "data.frame")
  </code></pre>
  
  <p>I have customised the colour palette using the code below.</p>
  
  <pre><code>getPalette = colorRampPalette(brewer.pal(9, "Oranges"))
  getPalette(colourCount)
  </code></pre>
  
  <p>I then produce the below plot with accompanying code.</p>
  
  <pre><code>plot &lt;- ggplot(preseason18) +
    geom_col(aes(x = reorder(Week.Number, Distance.18), 
                 y = Distance.18, 
                 fill = Week.Number)) +
    coord_flip() +
    scale_fill_manual(values = getPalette(colourCount)) +
    theme_classic()
  plot + guides(fill = FALSE)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/IGfWQ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/IGfWQ.png" alt="enter image description here"></a></p>
  
  <p>How can I sequence the colours so they're going from dark (highest value for <code>Distance.18</code>) to light (lowest value for <code>Distance.18</code>)? Does it have anything to do with <code>scale_fill_brewer</code>?</p>
  
  <p>Any help will be greatly appreciated. Thank you.</p>