Explain why does colour of $KMnO _{ 4 }$ disappear when oxalic acid is added to its solution in acidic medium?

When oxalic acid is added to acidic solution of KMnO _{ 4 }, its colour disappear due to the reduction of MnO _{ 4 } ion to {{Mn}^{2+}}. Chemical reaction occurring during this neutralisation reaction is as follows: