(ScientificAmerican) - We can see millions of variations in color but we split up the rainbow into just six main colors when trying to describe what we see–red, orange, yellow, green, blue, purple. For the thousands of odors that we can smell we have barely any words at all, usually resorting to simile–smells like fresh cut grass, lemon, wet dog, stinky cheese. Chemists, sensory psychologists, and snobs of all types have been trying to define and categorize smells for decades, settling on seven main categories: musky, putrid, pungent, campohoraceous, ethereal, floral, pepperminty.