Answer: Colored Bands
If you’ve ever peered closely at the resistors found on the interior parts of many of your household electronics, you may have noticed their tiny stripes. Those color bands, known formally as the Electronic Color Code, serve to indicate the resistor’s resistance value.
The system was developed in the 1920s by the Radio Manufacturers Association (an organization now known as the Electronic Industries Alliance) to help easily distinguish the values between otherwise often indistinguishable resistors. The color and order of the bands on a standard four-band resistor serve to indicate significant figures of the resistor’s value (the first two bands), as well as the decimal multiplier (the third band), and the tolerance of the resistor (the fourth band). To a layman, the band system seems quite arcane, but to a well-versed professional or serious hobbyist, the band system is second nature.
While this system of color-coded bands has prevailed for the better part of a century now (and will likely continue to do so for non-surface-mount resistors), the advent of tiny surface-mount resistors—often hardly bigger than a grain of rice—has led to an increase in alpha-numeric coding in place of the banding method.