This strange effect of mist I saw once while cycling to work (it is actually clearer to see on the thumbnail). It was so strange to me that I thought it was worthwhile stopping and taking a picture. Since the colours are missing it cannot be a rainbow, but I guess it is a related effect. The picture was taking with the sun in the back and as you can suspect I just cycled out of the mist. If somebody can explain me more about this, please be my guest, my mail address can be found at home.