Make another duplicate of the same puzzle piece that is under the a and r. With the duplicate puzzle piece on top, select the puzzle piece and the Xara X logo and from the Arrange pull down menu, select Combine Shapes > Subtract Shapes to remove the shape of the puzzle piece from the Xara X logo.

(Actual size) Select the puzzle piece that was under the ar and change the fill to a Linear Fill (select Linear from the Fill Type drop down list with the Fill Tool selected).

Make the starting color 20% black and the end color white. Angle the fill path as shown.

NOTE: To apply a color to the fill path, click on either square at the end of the path and then click a color on the screen palette. To reposition the fill path drag either end.