Resistance values are often indicated by color codes, Resistor color code is identification of that resistor’s resistance, some resistor is very small in size and some very big but its value can be easily identify based on colors draw on it.
Virtually all the main resistors up to one watt are marked with color strips. The coding is defined in the international standard IEC 60062. This standard describes the marking codes for resistors and capacitors.
These also include numeric codes, for example, often used for SMD resistors. The color code is given by several bands. Together, they specify the resistance value, the tolerance and, sometimes, the reliability or failure rate. The number of bands varies from three to six. At least two bands indicate the resistance value and one band serves as a multiplier. The resistance values are standardized, these values are called preferred values.