The color of a cloud is primarily determined by its thickness and the amount of sunlight it reflects. Dark stratus clouds simply indicate that they are thick enough to absorb most of the sunlight passing through them.

However, depending on the specific appearance and associated weather, there might be other terms used:

* Nimbostratus: If the stratus clouds are dark grey and associated with continuous rain or snow, they are called nimbostratus.

* Altostratus: If the stratus clouds are high in the sky and appear a slightly bluish-grey color, they are called altostratus.

Remember, the basic cloud type remains "stratus," and the specific terms are added to describe variations in appearance, altitude, and associated weather conditions.