1) The pads on the strips are yellow when they are made.  If they are not yellow then they have been exposed to heat, humidity, light, or some other detrimental condition.

2) The test strips will change color outside the pH range shown on the color chart. The strips will turn purple in alkaline waters.  There is a way to check this.   Concentrated bleach will turn the strips purple and then yellow and then white as the paper bleaches out.  Dilute bleach will turn the strips purple and then eventually a greenish color if they sit out for a few minutes.  In acids, there isn’t as much change.  When testing vinegar (dilute acetic acid) they should remain yellow.  I have tried the strips using both concentrated and dilute acetic acid – both were yellow.  You might try adding a little vinegar or bleach to small samples of the water to confirm that the strips react as expected.

3)  Temperature has a slight effect on the test results.  It seems that raising the temperature from 25C to 70C causes the color to shift about ½ a color unit higher.

4)  When testing RO, distilled, or tap water, the strips might not behave as one might expect.  The indicators used with the strips require that the waters being tested have some buffering capacity.  RO and distilled waters have little or no buffering capacity and the strips will not work in these waters.  If the tap water has a very low buffer capacity (low hardness, low alkalinity, etc.) the color can take much longer than the recommended 1-2 second immersion and 10-15 development time.  We ran a test to find results on various buffer solutions with the color transitioning from yellow to purple from pH 4-7 in 0.5 unit increments.  These particular buffers did not develop very intense colors in the pH 5-6 region.  The shades were close but the intensity was not as intense as the color chart.  We would expect that the mash has sufficient buffer capacity.

Since the color of the strip remained yellow, that would seem to indicate that the pH was lower than 4.5.  If this is not what you would expect we would suggest two things:

1)  Try the bleach test described above in item (2) to make sure the strips are reacting like they should.  If they do not turn purple, then it is possible that the strips are old.

2)  Try a fresh vial of strips.