Place well-rinsed beans in a 4-quart pot and cover with several inches of water. Discard any beans that float to the top. Soak the beans for 4-12 hours.
Discard the soaking water, leaving just the beans in the pot. Add the 6 1/2 cups of water and the bouillon granules. Bring to a boil over high heat. Reduce the heat to low, cover, and simmer for 1 1/2 hours, stirring occasionally, until the beans are tender. During cooking, the beans should be just barely covered with water. Add a little water as needed.
Add the onions, bell peppers, salsa, garlic, chili powder, cumin, and oregano. Cook for 30 minutes or until the beans are easily mashed with a fork and the soup is thick.
Remove 2 cups of the soup to a blender. Puree until smooth. Return the mixture to the pot and mix well. Cover and simmer for 5 minutes. If the soup is too thick, add a little water.
Top each serving with a dollop of sour cream, green peppers, and onions. Serve over brown rice, if desired. Serve hot.