There are three colors -- red, blue and yellow - that cannot be made from other colors. Thus, they are called primary colors. All other colors are created from various combinations of the three. Black, the absence of color, is used to darken colors; and white, the combination of all colors, is used to lighten them. The two basic colors of 3D glasses are red and blue. When looking through the blue lens, the eye filters out all of the blue colors of the image. 3D movies are made to feed different images to each eye, one taken at a different perspective than the other. So, when the blue and red are filtered out to each eye, the object gains depth.
The primary color, red, is usually found as one lens of 3D glasses. The colored lens filters the red out of anything that you may be looking at, and your eye perceives the image as having no red tones. When all of the red is filtered out of an image, the opposite color on the color wheel, green, is enhanced. The earth has the appearance of being a healthy place when it flourishes in green, thus one of the reasons people use the adage "looking at the world through rose-colored glasses" is because of the illusion of lush green that the red-filtered glass provides.
Green is used as a lens occasionally in 3D glasses instead of blue. On the color wheel, it is the opposite color of red. When the colors red and green are mixed together, they cancel each other out. If you were to stare at a red object and then look away at a white piece of paper, the object would appear in green. 3D movies take advantage of the optical illusions produced by our brains.
Cyan is a light green/blue. Working on the same principle as green in the 3D illusion, the manufacturer of the 3D glasses may make the red a lighter color for safety reasons. (It may be safer for people--such as children who want to run around while wearing them--not to look through dark colored glasses.) To compliment the lighter red, the lighter color of blue and green, cyan, is used.