Update documentation of colors on Status.

site/dev/testing/buildbot.md

 Skia Buildbots
 ==============
 
 Overview
 --------
 
 Like the Chromium team, the Skia team uses [buildbot](http://trac.buildbot.net/)
 to run continuous builds and tests.
 
 Here is a link to our main status page: https://status.skia.org/
@@ skipping 52 matching lines @@
     * One or more Builders may run on a given Buildslave, but only one runs at
       a time.
     * One or more Buildslaves may run on a given host machine.
 
 
 Status View
 ------------
 
 The status view shows a table with builders, grouped by test type and platform,
 on the X-axis and commits on the Y-axis.  The cells are colored according to
-the status of the build for each commit: green indicates success, red indicates
-failure, light orange indicates an in-progress build, and white indicates that
-no build has started yet for a given revision. Commits are listed by author, and
-the branch on which the commit was made is shown on the very left.
+the status of the build for each commit:
+
+* green: success
+* orange: failure
+* purple: exception (infrastructure issue)
+* black border, no fill: build in progress
+* blank: no build has started yet for a given revision
+
+Commits are listed by author, and the branch on which the commit was made is
+shown on the very left. A purple result will override an orange result.
 
 For more detail, you can click on an individual cell to get a summary of the
 steps which ran for that build.  You can also click one of the white bars at
 the top of each column to see a summary of recent builds for a given builder.