Vinegar with universal indicator added. Universal indicator changes colour depending on whether it has been added to an acid or an alkali. Vinegar mainly comprises a solution of ethanoic (acetic) acid. In acidic solutions, as seen here, universal indicator turns a colour between red (strong acid) and pale orange (weak acid). In alkaline solutions, it turns between green (weak alkali) and purple (strong alkali).
Model release not required. Property release not required.