Go into edit mode of an article

Click on the table and right click mouse button and select table properties
 
Click on the Cell Properties Tab



Highlight the cells you would like to add a background colour
 
To highlight more then one cell hold down the Ctrl button while selecting the cells
 
When you have highlighted the cells
 
Select the background colour function and select the Colour or you can Add a Hex Colour
 

If you are adding a Hex Colour select the Add Hex Colour function and in the box enter the hex code eg #DFF4FF and press OK