Click Shape Fill, and under Theme Colors, pick the color you want.
Select the shape or text box.
On the Drawing Tools Format tab, click Shape Fill > More Fill Colors. In the Colors box, either click the color you want on the Standard tab or mix your own color on the Custom tab.
Or
Right-click on the cell(s)
Select "Format cells"
Click on the "Fill" tab
Click on "Fill Effects ..." (below the color grid and above "Sample")
Select the two colors you desire
Select "Diagonal Up" or "Diagonal Down" under "Shading Styles"
If this does not work due to different formatting you'll have to recreate the whole table & repeat these methods.
