The color scale for the 0-100 ppm peroxide strip is very dependent on the pH of the solution being tested.  The test pad on the strip is buffered in the range of 5.5-6.0.  The capacity of this buffer system should be sufficient to keep the pH in that range for diluted, water-based peroxide solutions.  The enzyme used in the test pad, which in conjunction with an indicator and the peroxide, produces the blue color on the scale in proportion to the level of peroxide present. This enzyme is most effective in a pH range of 5-7.  Solutions with pH below 5 and above 7 significantly reduce the activity of the enzyme and may result in colors that do not match any on the color chart.  If possible, adjust the pH of solutions being tested to the 5-7 range before using the strips.  Make sure to take any dilution into account when arriving at the final peroxide concentration.