this is inconsistent with all other goods where the dark green means you have extra production capacity available that is currently used
here i have 77% because not enough people are in range of the post office, this is completely different, i have no immediate way of increasing the population in range -- there are NO more people on the island! (yes i realize you're simply dividing in-range population by 500)
EDIT:
post office covering 638 out of a total 1155 jornaleros-only population on the island: 128%? 127%? make up your mind...
and current of 2 out of potential of 1?