I believe that the word goodwill is used metaphorically here. Goodwill here means, the benevolence of the brain. Which means that if the different parts of the brain work together, and efficiently, like they are doing you a favor, only then will you be able to experience all these things (color, movement, depth, etc).
If however, even one of the parts of the brain refuses to cooperate, then they 'knock out a single thing', which means that there is some sort of disability, in experiencing these things. Knocking out color but nothing less refers to perfect vision with color blindness. You can see, but cannot see color. SO the color blindness is the 'single thing'.