Google Pie Chart: How to remove the white line between slices?

Use a configuration parameter pieSliceBorderColorwith a value transparent( see documentation here ).

  new google.visualization.PieChart(document.getElementById('visualization')).
  draw(data, {
                pieSliceBorderColor : "transparent", // Add this line
                title : "So, how was your day?"
              }
      );

Before:

After:

Spell: http://jsfiddle.net/PWc43/