The only thing one ever sees are colored things. Physical objects have no color. Therefore, one does not see physical objects. If an object consists entirely of parts that have no color, then that object has no color. All physical objects consist entirely of elementary particles.
Elementary particles have no color.
Therefore, physical objects have no color. According to Russell, the theory of an objective, physical world explains aspects of the sense data that we experience. Here is one hand. Here is another. Therefore, there are external objects.