Changing leaves

On Tuesday we finally left the animal world and turned to plants,  I am really going to miss the dissections though.  Our experiment Tuesday was to show how leaf color is affected by different ph levels.  It was a pretty simple experiment, we boiled some red cabbage so the water took on a bluish color then added various amounts of ammonia (a base) and vinegar (an acid).  As we put more in the water showed a broad range of colors going from pink to green.  We would put in one of the ammonia or vinegar and watch it change color, then put in some of the other and reverse it back again.  

When I think about it, I wonder what explanation evolution has for this.  How does this change help the plant survive?  Evolution says that organisms survive by developing traits that make them stronger, well, how do beautifully colored leaves make that tree stronger?  The way I see it is that the only explanation for this phenomenon is that it was created by a loving God who seeks to fill our world with beauty!