The most basic camouflage is the sort worn by soldiers on the battlefield. Conventional camouflage clothing has two basic elements that help conceal a person: color and pattern.
Camouflage material is colored with dull hues that match the predominant colors of the surrounding environment. In jungle warfare, camouflage is typically green and brown, to match the forest foliage and dirt. In the desert, military forces use a range of tan colors. Camouflage for snowy climates is colored with whites and grays. To complete the concealment, soldiers paint their face with colors matching the camouflage material.
Camouflage material may have a single color, or it may have several similarly colored patches mixed together. The reason for using this sort of pattern is that it is visually disruptive. The meandering lines of the mottled camouflage pattern help hide the contour -- the outline -- of the body. When you look at a piece of mottled camouflage in a matching environment, your brain naturally "connects" the lines of the colored blotches with the lines of the trees, ground, leaves and shadows. This affects the way you perceive and recognize the person or object wearing that camouflage.
Human perception naturally categorizes things in the world as separate objects. When you look at a scene, you are gathering an immense amount of information with your eyes and other senses. In order for your conscious mind to make any sense out of this information, your brain has to break it down into component parts. When your brain perceives a long, vertical area of brown with green blotches connected to it, you perceive a tree. And when your brain perceives many, many individual trees in a given area, you perceive a forest.
One thing your brain is always looking for when analyzing visual information is continuity. Imagine a stack of 12 blocks. If all of the blocks are colored red, you perceive the pile as one unit. But if the bottom six blocks are red and the top six blocks are blue, you may perceive the pile as two separate units: a stack of blue blocks on top of a stack of red blocks. And if you were to randomly mix blue blocks and red blocks together, you wouldn't group them into colored units at all. We tend to recognize something as a separate object if it has one continuous color, so a person is much more likely to stand out when wearing a single color than when wearing a jumble of colors. In the jungle, you perceive the jumble of colors in camouflage material as many small things that are component parts of the surrounding foliage.
In this way, mottled camouflage helps people go undetected even though they are in plain sight. Once you have spotted a camouflaged person, he stands out, and it seems odd that you didn't see him before. This is because your brain is now processing the visual scene differently -- it is looking for a single person.
Camouflage is not only used to hide people, of course. In the next section we'll see how military forces use camouflage on a larger scale, to hide forts and heavy equipment.