Angels with very light stripes...

Stripes on Angelfish and Discus often change intensity like this, whether it be from stress, the overall background color of the tank, or even a simple change in lighting. It's normally not something to worry about unless you are seeing other signs of illness. It's also theorized that the stripes can change intensity as a form of communication between fish.

My thought on this is that when you first introduced your fish they had nice dark stripes as a camoflauge response, as they got used to their surroundings they became less stressed and there for lightened in color.

A lot of my really settled angels seemed to have become lighter. I often take it as a sign they are happy. Never show stress colors unless excited by food dropping in.