Why is Neptune the darkest planet?

Neptune is known to be a dark planet probably because the heat of the sun does not reach it too much anymore. This is a cold planet with a temperature that may be increased further because of the very strong winds. One thing that is unique about Neptune is that it has a moon that has an opposite rotation from the usual rotation of the planet.

This is unique as this is a quality that cannot be seen in other planets. Neptune is known to have a sort of greenish hue because of the amount of methane that can be found in its atmosphere. The dimmer illumination is due to its distance from the sun.