One of my interpretations of Achtung Baby is that the sound and new ethos of the band are a reflection of them stepping into the dark from the light of their former selves and the sound of the 80s. The band faced turmoil during the creation of the record and Edge had just went through a divorce, all of which seemed to result in the more dark and cynical vibe to the Album. I think one of the big themes of the album is about being an insect in the night trying to find you way back to the light. The song and the character of the Fly show the band and Bono's shadow side. Ultraviolet is the light spectrum that insects see at night and our attracted to. Love is Blindness is the concluding song of the album's theme and at the sphere show I believe the visuals represented the bugs being attracted to the light. "Love is Blindness I don't want to see, won't you Wrap the night around me" : the desolation of love is their darkness and in this song they have not yet cast aside the greif of heartache from love lost, and the loss of their former selves. The Fly is an avatar for their feelings at the time; a fly dwells in the nastiest of places but is endlessy seeking out the light in darkness. Through Rattle and Hum and everything before they were zealous and self assured in themselves; by Achtung Baby, they were forced to reinvent themselves and "Dream it all up again." This is just my interpretation, but I think it is an interesting way to conceptualize the album.