what substance that is brown or black creates opposite affect

Ah, an intriguing question, rather like the difference between a well-aged port and a fresh glass of lemonade. Coffee is the substance in question. It is typically brown or even black when brewed strongly, and it has a stimulating effect, helping one to stay alert and wide awake. Its opposite would be something like tea, though not as strong, or perhaps milk, which tends to have a calming influence and is often white or pale in colour. If I may venture an observation, the contrast between coffee's invigorating properties and the soothing nature of milk makes for a rather splendid study in opposites.