Why is a colour code used for resistors?
in practice, it is much easier to read the color codes than the letters of the standard resistance values for two reasons: the color codes are printed around the device, so you never have to turn the table for read the values, and second, after a while, you tend to read them as words. it’s a bit harder to explain – with experience, you recognize patterns like, for example, orange-orange is worth 33. Therefore, if you’re looking for a 3.3k resistor in a bunch of resistors, it’s easier to search for an orange-orange. then confirm that the next color is red, then look at the resistors of the same color and try to read the value printed on it. note that this only works because we only have a handful of standard values. you will notice that the resistance is printed in alphanumeric characters on the precision resistors (those with 0,1% tolerance) which are presented under one hundred different values.
it was much easier to print circular rings around the cylindrical object in this case the resistors. more importantly, during assembly, it was always possible for the resistor to be assembled with the value under the resistor itself.
On the other hand, painting the rings around cylindrical bodies is much easier. the international color coding system came later.