When he was 26, Gaudi wrote in a diary, "The ornamentation has been, is and will be coloured. Nature does not produce anything that is monochrome or uniform in color: neither vegetation nor geology, nor in topography nor in the animal kingdom. The contrast in colour is always more or less alive and from this we are obliged to colour in part or all of an architectural piece, colouring that will perhaps disappear when the hand of time gives it another colour that is more befitting and precise for something old".

Antoni Gaudi quoted by Juan-Eduardo Cirlot. GAUDI: AN INTRODUCTION TO HIS ARCHITECTURE.