The dark stools are of more concern than the red blood.
It sounds like you are being appropriately treated. When you get the colonoscopy try not to eat the full day before except for liquids. Don't cheat. And drink a lot of fluid. The cleaner the passageway the better the imaging.
My advice is to make your appointment and follow your physician's dietary recommendations.
Good luck.
Diverticular disease simply means the presence of little pockets in the bowel. When these pockets become inflammed thats called diverticulitis (rule of thumb, anything ending in 'itis' is an inflammation).
This inflammation can be caused by faecal matter getting into the pockets (diverticuli) and staying there. There is treatment for the inflammation but no cure for the diverticular disease itself other that managment to prevent inflammation. its mostly important to prevent constipation. Usually you will be given diet advise, such as avoid seeds as they get stuck in the bowel pockets etc. the colonoscopy is booked to outrule other causes of your symptoms, and is usually a precaution. It would be careless not to book you for one! You havnt mentioned if you have a temperature, but once you have no vomiting or diarrhoea, then the small amount of blood can be due to trauma within the colon which can be cause by the inflammation. The colonscoy will reveal everything usually