@Tigerrun777, thank you for including the picture! The blue portion behind the fence is a shadow and the orange semi-circles are bunting used for holiday decoration. The only odd thing I see is the rainbow like blob in the lower right corner.
Since you state that all your fences have this pattern, I would assume you mean the orange semi-circles. To get rid of that you can either use your decorations box to remove decorations (but this will remove all decorations , such as twinkling lights on your roof), or you can have your Sim interact on the decorations box to choose another decoration for just your fences!
Please reply back If you have any problems or questions about this!
ok thanks very much I forgot about the seasons pack. I did not know the roof got decorated for christmas too. Geez that is a relief now I know what happened. Its good to know why this was happening and its not a glitch phew thanks.
@Tigerrun777, you can let the game decide what decorations to place on your house or you can pick them one by one for each of 5 categories: foundations, roof eaves, fences, spandrels, and friezes. (you are less likely to have friezes and spandrels.) Either way you decorate , the action will be done by clicking on the decorations box!