universal indicator 
noun [mass noun] Chemistry
A mixture of dyes that changes colour gradually over a range of pH and is used (especially as indicator paper) in testing for acids and alkalis.The easiest universal indicator to prepare is red cabbage juice....
- The groups are regular acid-base indicators, mixed indicators, screened indicators, universal indicators, pH sticks, litmus paper (embedded in gel or litmus in a gel), natural food indicators, fluorescent indicators, luminescent indicators, irreversible indicators and a miscellaneous group.