Transmission – additive color

Light sources can be a single color or multiple colors – which we refer to as "white light". We can make a single color light source from a white light source by placing a color filter in front of it.  Some things that transmit light emit only one or a few colors.  

RGB primaries

To make sense of colors we identify three colors that all other colors can be made from. These are known as Primaries. When we transmit light, the primaries are known as additive. As we add them together, their combination tends towards white.



The most common transmission of primary colors is in cathode ray tube and plasmas display systems, like the one on your computer, phone or television. These three colors were first used in color televisions as three emitters, one for red, one for green and one for blue. Later plasma and LED technology put millions of small emitters of red, green and blue on a surface of a display. BY transmitting these three colors, the display can show millions of colors by tricking our eye into combining them.

In the early days of computers, television sets were converted into color graphics displays. In order to make programs that could ask for a certain color in a certain place, a numbering system known as RGB began to be used. RGB took three numbers, one for each primary, and specified a color. The early desktop computers could only use numbers between 0 and 255. Anything bigger required some trickery to get the numbers to work. So these first systems used 0-255 to measure the relative amount of color in the R, G, and B primaries as separate numbers, a system that has stuck with us today.  Sometimes instead of 0-255 software may use 0 -100%. In either case 0 means no color and 255 or 100% means all the color.

For computer scientists however, working in base 10 numbers (0,1,2,3,4,5,6,7,8,9) was much more difficult than working in hexadecimal numbers (0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F) where A stood for the decimal 10, B stood for 11, and so on. 0 to 255 in hexadecimal could be written 00 to ff. Most computer scientists will put a # sign on front of a hexadecimal number to let you know it is one. #0F would be fifteen for example.



When computer systems got more complex, the three numbers got combined into a single hexadecimal number. If you ever happen to see something like this in web design:

background-color:#0000ff;


#0000ff is a color where there is no red or green but all blue, so it is blue. These numbers can be broken down into two digits each of #red-green-blue.  So for example these are the representation of some simple colors:


These colors can also be mixed to any value between 0 and 255, so for example a simple light skinned flesh-tone palette might be (later on we'll explain why):  



A six digit hexadecimal color can describe 16,777,216 colors, enough to keep anyone busy.  While web based colors have gone to a single hexadecimal integer, more sophisticated programming software development environments, such as Java and Objective C, have gone to three real numbers for RGB, meaning infinite color combinations.