Substrate and background color have a huge impact on both the color and behaviour of discus, in my experience. I had a dramatic black back ground [looked great with the plants] for a few years and then switched to a light blue. I had medium brown type gravel and switched to light buff silica sand at the same time I repainted the background on my show tank.
The primal drive for discus [for all of us beings on the planet] is safety, of course. Thus, discus try to blend into their surroundings so as not to attract a hungry predator...If the background/substrate are dark, your discus will go in that direction; the reverse is also true. Dependent on the strain of the discus, you will see permutations of this. Examples would include: in a dark situation, barred discus show their stripes more dominantly and pigeon blood varieties will show significantly more peppering [grey/black schmootzy dusty little dots]. Behaviour wise, my discus became more gregarious and active when I lightened up the tank. Their color presentation improved drastically-- the turqs looked more relaxed and better colr, the blue pigeons cleaned up, I had blue fish that I always thought were perplexingly slightly unwell that in reality were fine, just trying to blend in to the old dark look of the tank, as it turned out. They are brilliant in comparison since the updates. Just my two cents.
Bet regards
Harriett