HIn + H2             H3O+  + In-
Acid-base indicators are weak acids or bases.

The molecular form has a different color
than the ionic form.
HIn + H2             H3O+  + In-
HIn + H2O          H3O+  + In-
Increase the concentration of H3O+
HIn + H2             H3O+  + In-
HIn + H2O          H3O+  + In-
Decrease the concentration of H3O+
Or