Fixed: Graph/Chart generation selects slice/background color identical to text color (bug#6323).
Squashed commit of the following:

commit 16d27c25b23c2c0ba0e3f81a1a632750b42355b1
Author: s7design <otrs@s7designcreative.com>
Date:   Tue Feb 4 09:51:05 2014 +0100

    [Bug 6323] Graph/Chart generation selects slice/background color identical to text color

    Deleted black color  for the graphs (Stats::Graph::dclrs) in config XML file, and also deleted black color from list of default color in Stats.pm.

    Note:
    This only define default list of color, but if user want, he can define black colors for the graphs.