Cut the kernels off of the corn cobs and add them to the blender. Add the yellow bell pepper, green onions, garlic, half of the sour cream, buttermilk, and half of the chili powder. Season with salt and pepper to taste. Blend the mixture until it is smooth.
Serve immediately topped with some more sour cream, cilantro, and chili powder or store in the refrigerator for up to three days.