As explained by Arduino to Go, each color band on the resistor corresponds to a number but this can differ depending on the band's placement.It's not complicated, but the sheer number of colors ...

The color code was very useful in quickly identifying a resistor’s value. It’s simple, and straight forward. But you have to make a little room in your brain to remember this stuff.

We’ve all been there. A big bag of resistors all mixed up. Maybe you bought them cheap. Maybe your neatly organized drawers spilled. Of course, you can excruciatingly read the color codes one… ...