The white light spectrum is made up of six primary colors that are ordered in a certain order: red, orange, yellow, green, blue, and violet. Newton realized that a beam of light of a specific color is always deviated by the same amount, but he did not appear to comprehend why. He speculated that all colors would be split into seven sub-colors if they were separated by thin glass plates.
Newton's idea was wrong but his intention was right: he wanted to explain how colors work. In fact, all colors need not be divided into seven sub-colors to produce all possible colors; instead, they can be thought of as different frequencies of vibration of the same basic color - red, for example. If you play two notes on a piano that are one octave apart, you will see that they do not sound exactly like the first note you played because they have their own unique frequency. These frequencies combine to form new frequencies that you cannot hear separately but that lead to the appearance of whole new colors in your mind's eye.
When you look at an object, only three of its colors are actually seen by your eyes. The others are assumed by your brain based on how it associates colors with things it knows well. For example, if you look at a red apple, your brain assumes that there must be more red things around than apples that are other colors, so it makes some extra black bits appear on the image in front of you.
These colors can be mixed to create almost any color in the visible spectrum. For example, red and green make purple, blue and yellow make gold, and all together they make white.
Furthermore, blackbody radiation exhibits these same six colors, but in reverse order (violet, then blue, then green, then yellow, then orange, then red). Thus, blackbody radiation is an example of "complementary" color mixing - colors that will mix to give a complete absence of color (i.e., black) when exposed to sufficient amounts of each other.
Finally, white light has been shown to contain frequencies at least as high as those present in red, orange, yellow, green, blue, and violet light. Therefore, it can be said that white light contains everything there is to see with human eyes.
As mentioned above, blackbody radiation also contains every color in the visible spectrum, but in reverse order. This implies that if you were able to expose human eyes to only the wavelengths contained in blackbody radiation, then those eyes would perceive all the colors in the visible spectrum simultaneously!
Newton first classified the spectrum into six distinct colors: red, orange, yellow, green, blue, and violet. He based this classification on how well plants grow in these colors of light.
It is now known that the spectrum of colors of sunlight is much more complex than this simple diagram shows. However, Newton's work laid out a framework for scientists to understand how different parts of the spectrum affect life on Earth. Today, we know that there are also important wavelengths outside the visible range that play a role in photosynthesis (inferred from experiments with plants in laboratories). These invisible wavelengths come in two types: long-wave infrared and short-wave ultraviolet.
Infrared waves are like the heat radiation given off by an object when it is warmed by the sun or burned by a match. The human body also emits infrared waves when it gets hot. Objects that are rich in carbon such as trees, leaves, and oil paint reflect most of the infrared energy from the sun back to space. This is why forests tend to be dark at night and why tall trees can block solar power from reaching the ground. Vegetables and flowers cannot resist infrared radiation so they are bright in the daytime and become darker at night.