The dominant feature of his paintings during this period – which he referred to as “fixed structures with a chromatic licence” – is the dialogue they create between the “colour-sign” and the monochrome background. In some cases, thin, taut lines crowd together, populating the entire surface, which may be square, rhomboidal, triangular or round, while in others the signs follow on one after the other in perspective. 

Another key theme in this series of works is that of sentiment, and of love in particular, which is experienced both as a sexual drive and as a romantic desire. Works like Dal tempo totale: le strutture fisse con licenza cromatica: l’armata rossa vincerà, 1969, Progressione di un rosso, 1971, Trilogia dell’amore, 1973, and L’incontro 3, 1972, which was shown at the 10th Quadriennale Nazionale d’Arte in Rome in 1973, adopt a visual language that can be defined as reductionist. They came at the same time as the studies by artists such as Joe Baer and Agnes Martin and they reveal a personal story line and a need to talk about love that Nigro never lost. Indeed, it remained the most important source from which he drew inspiration, as he himself later stated: “At a certain point I need to sing, I need to paint, I need to do something. It is the reflection of a need for love, irrespective of any manifest tragedy or drama”.