I would say they are not decorative on both sides, but the plastic the stickers are printed is see through and not white. If I remember right, you can see the fish on the sticky side, but it is not as vibrant. Kind of hazy I guess.
I agree with previous answers about the colors are muted on the back side. I have a caution against using these on a window. In my son's room there's 2 outer walls that have temperature fluctuations, and when I had to remove some, they took the paint along with them (whereas ones on the inner walls had no problems). So, on windows, you might have to remove adhesive when taking them down.
They are decorative on both sides... Though the image clearly has a front and a back. They don't look as nice from outside of the window looking in. But they are much less cloudy on the edges than other clings. Hope this helps!