This is what we called pH indicator paper. The pH 0 to 14 will be indicated by contrast of paper color. Macherey Nagel maybe the manufacturer of this pH tester. Sometimes we use this stick tester to measure and compare reading with our own instrumentation analyzer.
pH Indicator Paper Macherey NagelMeasurement of pH value is possible even in unbuffered or very weakly buffered solutions, since the sticks can be left in the solution until the final colour change is completed.