When system appearance is set to Graphite, WebKitTestRunner respects that, and draws pixel results with a different color. Not sure why these settings were omitted, DumpRenderTree "always" had them.
Created attachment 209922 [details] proposed fix
Comment on attachment 209922 [details] proposed fix Clearing flags on attachment: 209922 Committed r154805: <http://trac.webkit.org/changeset/154805>
All reviewed patches have been landed. Closing bug.