Several of Vaughan’s works of this period possess titles that, at first, seem puzzling. The on-looker here can be identified as the pale, almost ghost-like figure (suggested rather than fully realized) at the upper right. He is gazing towards the foreground group. His unexplained separation and isolation from the others, (something that Vaughan himself frequently experienced), creates the emotional tension within the composition.
Vaughan’s finest gouache decade was perhaps the 1960s when he produced numerous first-rate paintings in rapid succession. He made further technical breakthroughs in terms of handling his gouache with greater eloquence and determining his compositions with renewed confidence. The character of his paint became increasingly fluid and his touch more assured; the rigidity of the densely applied paintings of the 1950s gave way to a fresher and more articulate technique. (Vann and Hastings, Keith Vaughan, Lund Humphries, 2012, p. 168.)
These words certainly apply to The Onlooker since the handling of the pigment is fluid and eloquent. Gouache suited both Vaughan’s creative temperament and working method. It is a very immediate medium since it dries rapidly and, as a consequence, fosters speedy progress and spontaneous management. Vaughan is economical with his palette; only yellow, blue and burnt umber are employed, along with black and white, to achieve a highly expressive effect. The opacity of certain pigments is played off against the translucence of others and his characteristically frothy textures are also in evidence. The mark-making has the freshness of an improvisation. Vaughan explained his approach to painting in his journal:

‘I seem to be purposefully trying to make a composition of mutual contradictions. Figures which aren’t figures, landscape space which is something else, shapes which are neither abstract nor figurative. What am I doing and why? Certainly I am following a scent, but it is buried and extremely irrational.’ (Keith Vaughan, Journal, November 27, 1957).