Sounds normal to me - the older blooms are fading. More noticable in dark colors like you are growing.

Sorr, maybe I wasn't clear. The blooms to which I refer are new blooms. new blooms are coming on a lighter color.

It could be that the change in color is due to the change in soil, air temperature and sun exposure. My guess is that they will change back to the original color when they become aclimatized

ok thanks for your help!

I also just transplanted several deep purple/blue petunias from a nursery into hanging baskets where I had mixed 1/4 native soil with one part each organic compost, worm castings & an acid-loving potting soil. 1 week later I noticed that the edges of new & old blooms alike have a faded color and new unopened blooms are completely faded in color. Some almost getting a washed out pinkish hue. I had 4 plants leftover that were not transplanted and are still in the nursery containers. They are not showing any signs of fading and are noticeably richer in color & darkness. I am wondering if the ph of the soil & water is enough to cause this discoloration? Both the native soil and water here are very alkaline - water around 8.5 and soil upwards of 9. Anyone observed anything like this with petunias before? I will try to feed some acid solution of dissolved citric acid and perhaps some acid fertilizer and see what happens.