Purple ph test sample.

[Teapot]

A pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH (acidity or basicity) of the solution can be determined visually. Normally, the indicator causes the color of the solution to change depending on the pH.

No sh!t Sherlock

[dynamictiger]

A true purple blue can form in the presence of extreme high bromine. The bromine combines with the phenol red to form bromo-phenol blue. Someone with less experience may mistake this for extreme high pH, when in fact the opposite is the case. Be wary of this trap.