Bolivian rams (at least mine) are voracious eaters, gobbling down just about anything. I have five now, but I originally had seven Bolivian rams. The two that died stopped eating a couple days before they died (this occurred within three weeks of their introduction into my aquarium). And from my experience they turn dark when they are stressed. If you haven't yet, I'd recommend to try feeding frozen blood worms or dried tubifex worms. These are my rams' favorite foods.
If it continues to not eat even after treatment, and depending on your tank size, I would recommend buying a few more rams. It may be that the reason your ram is not eating is simply stress. They have interesting social behavior and will feel less stressed (granted there is enough space) in groups. If it's a 20 gallon (75L) tank, you could have two total (one male and one female). If it's bigger, say 40 gallons and up, you could have 3-5. Ideally, I've been told, a 1:2 male to female ratio. But, if I've sexed mine correctly, I have 3 males and 2 females, and they get along great.
Good luck with your Bolivian ram. Bolivians are by far my favorite dwarf cichlid that I've owned, and I would encourage you to not lose faith in this fish! They have beautiful colors (especially in groups), are incredibly hardy once established in an aquarium, and show great personality and social behavior.