General chemistry books will also have more examples. Although we discuss the metal concentration in solution, the metal really exists as an aquo complex. The NO 3 - is a spectator ion and we don't expect it to take part in any equilibrium. Water has two lone pairs of electrons on the oxygen and can form complexes with transition metal ions. We can think of complexes in solution being in competitive equilibria with other species.
Calmagite indicator has two -OH groups with acidic protons.
The color of calmagite changes depending on whether or not these protons are present. Calcium and magnesium ions can displace the protons to form a calmagite-metal complex. The color of the complex is red.