Hello there, Max,
I think you are refering to what's known as a choroidal nevus, or "eye mole." They're rare, and can only be seen by an eye specialist.
Everyone has specialized cells called melanocytes that are responsible for producing melanin, which is responsible for giving us our color. These melanocytes are located in different areas of the body, particularly the skin, hair, and lining of internal organs, including the eye.
The moles on the skin that we are all familiar with are caused by melanocytes producing a high concentration of melanin pigment in a certain area, thus the appearance of a dark spot. The choroid is a lining in the back of the eye between the retina and sclera. It's full of blood vessels, and delivers nutrients and oxygen to the outer layers of the retina. A benign (non-cancerous) concentration of melanin on the choroid is termed a "choroid nevus." Just as moles on the skin, in some cases, a choroid nevus can develop into a malignant melanoma.
A choroidal nevus rarely requires treatment, and there are no symptoms as long as they remain small. You should see your eye care physician at least once a year to make sure the nevus hasn't changed. Usually, your doctor will use photography to document the size and appearance of the nevus and compare it to the way it looks in future examinations. If the choroidal nevus has orange pigmentation, or is leaking fluid, or is thicker than 2 mm, it may be (or become) a malignant choroidal melanoma and require further treatment.
I hope I've addressed all of your concerns. If you have any further questions, don't hesitate to contact me.
***** *****, B.S., University of Georgia