Heat the grill. Combine the paprika, cumin, cayenne and ¼ teaspoon salt in a small cup. Brush the salmon with the oil and sprinkle with the spice mixture. Combine the sour cream, cilantro, green onions, lime juice, and ¼ teaspoon salt in a blender. Blend until smooth. Grill the salmon, covered, over medium heat for 4 to 6 minutes or until the salmon just begins to flake, turning once. Top the salmon with the sauce before serving.