Final answer:
Turquoise is not used in the resistor value colour code, which includes colours like black for 0, brown for 1, all the way to white for 9. Turquoise doesn't have a corresponding numerical value in this system.
Step-by-step explanation:
The colour that is NOT used in the resistor value colour code is turquoise. The colour code for resistors uses a set of colours to represent the numbers 0-9: black (0), brown (1), red (2), orange (3), yellow (4), green (5), blue (6), violet (7), grey (8), and white (9). The first two coloured bands on a resistor represent the first two digits of the resistance value, the third colour is a multiplier, and the fourth colour indicates the tolerance.
Clearer understanding of the analogy "goes from red to violet through the rainbow of colors" can be grasped when considering that if yellow were replaced by a different colour, the perceived sequence of the rainbow would not differ in terms of the ordering; however, the specific colour in question (yellow) corresponds to a numeric value in the resistor color code, so it’s essential for precision.