Colin had many exhibitions during his lifetime. Several major exhibitions were held under Arts Council of Northern Ireland Auspices. In 1969 he was awarded the M.B.E. Queen's University, Belfast conferred an honorary M.A. degree in 1972 and in that year he and his wife Kate toured extensively, visiting Australia. In 1976 John Hewitt wrote about Middleton, "I do not hesitate to describe him as the most various and imaginatively endowed of Irish Painters, past or present.

Colin Middleton continued to experiment with style and technique throughout his development as a painter. There were periods of surrealism, of cubist style, of extreme romanticism in which the influence of Yeats was strong and periods when the ascetic line and form of Ben Nicholson affected his work. It has been said of Colin Middleton's notebooks that they offer "evidence of an unsatisfied pilgrimage through the devious ways of modernism." But if Middleton's work displays such uncertainty, and it is a justified reflection of contemporary trends in art, the reflection is conveyed in work which, in each "period", displays great technical ability and a profound understanding of the unchanging material which forms the inspiration of his art.