Agree.
Color in Cyphotilapia is a behavior, not just a health and happiness indicator. The usual external factors affect their color, water quality, food, etc, but it's also normal for them to darken and lighten, even during the course of a day. The blue types may darken or lighten their bodies, darken and lighten their mask, shorten or lengthen their eye marking, darken or fade the mark under their chin in the case of Zaire blue, etc. Burundi types do something similar according to their more basic color pattern. Some do it more often or more extremely than others; in some moods some will go all dark or nearly all one color (fading their bars).
They tend to be affected by lighting, many show their best color in natural light, including sun coming through a window into the tank, and are less fond of bright overhead lights.
Curious-- Which type frontosa do you have? Tankmates? What do you feed?