Are there any other diseases besides Addison's that can cause darkened pigmination?

I am a 15 year old female. (5' 4"; just above 100 lbs if that makes a difference). I don't "lay out" that much or use a tanning bed yet I'm always tan. I find it hard to believe I have an olive complection because my family is pretty pale. I know Addison's Disease causes darkened pigmination. I also know that it would have to do with the adrenal glands, but that's all I know. I checked into Addison's Disease, but the symptoms don't all really seem to fit so I was wondering if anyone had any other suggestions of what it might be?