Merge pull request #1078 from ethanwhite/challengy-challenge

Add some color changes to Tree Biomass Challenge

exercises/Scientific-tree-biomass-challenge-R.md

@@ -18,4 +18,4 @@ species in a 96 hectare area of the Western Ghats in India using the data in
 [`ramesh2010-macroplots.csv`]({{ site.baseurl }}/data/ramesh2010-macroplots.csv)
 (if isn't already in your workspace then download a copy). Only include species
 with at least 100 individuals in your histogram, scale the x axis logarithmically,
-and provide good descriptive axis labels.
+make the bars purple with a black outline, and provide good descriptive axis labels.