Simple answer: yes. Under optimal conditions, 20 people could be exposed to the same patch of color which has a measurable, quantifiable value along the electromagnetic spectrum. However, due to variances in the visual system of each person (clarity of cornea, clarity of lens, clarity of the vitreous and aqueous humors, number of rods and cones in the retina, etc.) as well as 20 different ways to interpret the color, each person will see something slightly different. Try this: gather a group of friends--the more the better--at a paint store. Seek out a commercial product, any product will do, that has a STRONG singular color characteristic. Give everyone a good look at it for a while and then, one by one, send each person to the paint sample location and have them pick what they think is the same color from the samples provided. Don't show each other the samples until everyone has chosen. Then compare. Did everyone choose the same color? You may even want to compare it to the product you're trying to match and see who came the closest! This experiment may not produce much variance with a BASIC color like "fire engine red," but when you try it with colors that are harder to define--like "sea foam green" or "French vanilla"--you'll probably discover that everyone's perception of that color is slightly different.