To test for protein, you added Biuret solution and observed color changes. Suppose that the color data below was observed. A 3-column table has 1 rows. The first column is labeled Gelatin (+ control) with entry pink/purple. The second column is labeled
Water (negative control) with entry pink/purple. The third column is labeled Mystery food sample with entry blue.

The data above indicate an error. How do you know? What might have caused the error?