http://www.ncbi.nlm.nih.gov/pubmed/222080
Not sure if this well help, but according to this it seems ectopic ACTH can cause hyper pigmentation, but might be more common in pituitary ACTH.
Dont take my word on this, someone with a little bit more knowledge might be more helpful...anyone confirm this?
BTW good luck! dont freak out, u'll be fine!