Final answer:
The digit 6 in the resistor color code is represented by the color blue. The code is used to denote resistance value and tolerance on resistors. Adjusting a variable resistor connected to a bulb affects its brightness, not color spectrum.
Step-by-step explanation:
The color that represents the digit 6 in the resistor color code is blue. Resistor color codes use a series of colors to denote the resistance value and tolerance of electronic resistors. Specifically, the first two colored bands represent the first two significant digits of the resistance value, the third band is the multiplier, and the fourth band indicates the tolerance. When looking at a resistor with color bands, the blue color, in the position relevant to the digits, corresponds to the number 6.
In a related scenario, if a lightbulb is wired to a variable resistor, changing the resistance will not affect the bulb's color spectrum in the way described by the options given. Rather, increasing resistance typically results in a decrease in current, which would cause the bulb to become dimmer or, if the resistance is high enough, turn off completely. It does not cause the bulb to emit light of a different color.