Final answer:
In resistor colour coding, the colour yellow is associated with the digit B) 4. This coding is used to indicate the significant digits and multiplier for the resistor's value.
Step-by-step explanation:
The colour yellow on a resistor colour band represents the digit 4. In the resistor colour code, each colour corresponds to a specific number. When determining the value of a resistor, the first two colour bands represent the first two significant digits of the resistor's value, the third colour is the multiplier, and the fourth colour denotes the tolerance. Therefore, if the first or second band is yellow, it translates to the digit 4 in the resistance value.