Vinegar is an acidic solution which makes universal indicator solution (U.I.) red. Lime water colours U.I. blue. Such solutions are called alkaline.
* Photo left of the arrow: 3 drops of lime water with one of U.I.  are combined on a white plastic surface.
  1 micro drop of vinegar is also transferred by an Insulin syringe.
* Photo right of the arrow: The same samples are mixed in one big drop by an insulated copper wire.
Observation: The lilac colour of the indicator shows the alkaline reaction of lime water, the yellow colour of the indicator shows the neutral ( = not acidic, not alkaline) reaction of the mixture.
Explanation: The alkaline reaction of 3 drops of lime water was cancelled by the acidic action of 1 micro drop of vinegar. Such a chemical reaction is called a neutralisation. ( Lime water must be a very weak alkaline solution because  1 micro drop (5 µl)  of vinegar was sufficient for the neutralisation of 3 drops (100µl)  of lime water.)