Fix background color in Word export

- Specify background color using the fill property
instead of color property of a shading object.

Change-Id: I33127e08dcb11551d001a96bb658f7abe1c4c780

Src/xWorks/WordStylesGenerator.cs

@@ -617,9 +617,10 @@ private static StyleRunProperties AddFontInfoWordStyles(BaseStyleInfo projectSty
 			System.Drawing.Color backColor;
 			if (GetFontValue(wsFontInfo.m_backColor, defaultFontInfo.BackColor, out backColor))
 			{
-				// note: open xml does not allow alpha
+				// note: open xml does not allow alpha,
+				// though a percentage shading could be implemented using shading pattern options.
 				string openXmlColor = GetOpenXmlColor(backColor.R, backColor.G, backColor.B);
-				var backShade = new Shading() { Color = openXmlColor };
+				var backShade = new Shading() { Fill = openXmlColor };
 				charDefaults.Append(backShade);
 			}