Phenol red changes color twice in this experiment, it goes from red to yellow back to red. At the end of the experiment, the phenol red in the Elodea tube under light will be a different color than the elodea tube wrapped in aluminum foil. Why does the color change for both changes in the phenol red? Explain which specific metabolic cycle and compound causes a color change in one elodea tube but not the other. What is happening in this cycle that causes color change? This is a pre-lab question.