In my experience, cichlids in general are more colorful in dark environment. Glaring lights and white substrate and background make them look washed out.
Yes a darker substrate and a darker background can really make the colors of you fish pop, but if you go too crazy it can make the fish REALLY dark, so you have to find a medium. Generally a tan to slightly gray substrate with a black background really makes the fishs colors come out the best.
You know there are some fish though that should not be kept in dark environment. Pigeon blood discus for instance unless you like the peppering that makes them uglier.=/
There are a couple of threads that show the difference in the CA/SA cichlid section, you can use the search function to find them. People have went to a dark substrate and the fishes colours seem to pop.
A black background definitely helps to make colours stand out, unsure if it is the fish reacting to the background or if it is just because colours stand out against a dark background. I just know it works.
I can't tell you a personal example of substrate doing anything because I have always had darker substrates.