Hexadecimal Color Numbering System: We have seen how we can specify colors using the popup menus for fill color and stroke color, but it's possible to specify many more colors using what's known as the hexadecimal system.

Colors on a computer monitor are displayed by combining different amounts and intensities of the three primary colors red, green, and blue. A common system uses intensities ranging from 0 (no color) to 255 (full intensity). So a bright, pure red color would be red = 255, green = 0, and blue = 0 (255-0-0), while red = 150, green = 0, and blue = 150 (150-0-150) would be a medium purple, and so on. If all three values are 0, it gives black, and all three values at 255 is white. 

Instead of using the decimal (base 10) values 0 to 255 for this color system, however, computer scientists like to use a hexadecimal (base 16) numbering system, because the hexadecimal system correlates well with the binary (base 2) numbering system of bits (0 and 1 values) that is the foundation of computing systems. The hexadecimal system uses the values 0-9 and A, B, C, D, E, and F for its 16 digits. So the decimal numbers 0 to 255 end up being represented by the hexadecimal numbers 00 to FF.

Applied to the color numbering system, each color value consists of three hexadecimal numbers, one for red, one for green, and one for blue (in that order), each ranging from 00 to FF. So a color number might be "#A27C83", meaning red = A2, green = 7C, and blue = 83. The # sign in front indicates that the six digits represent a red-green-blue color combination, not some other number.