<p>Newton claimed to have proven the heterogeneity of sunlight by experiment. Olaf Müller argues that one could likewise prove the heterogeneity of darkness from inverting Newton’s experiments. Müller concludes that both, Newton’s proofs and his underlying methodology, are inconclusive and that Newton’s theory is underdetermined. This paper argues that Müller’s criticism is not justified because the conducted inverted experiments to which Müller refers do not replace Newton’s source of light with a source of darkness. Therefore, Müller does not refute Newton’s methodology, nor does he provide an example of underdetermined theories.</p>