His work can be divided into the 4 semi-autobiographical works of the Generation sequence; the two satirical black comedies Poppy, Mandragora and the New Sex, and How the Greeks Kidnapped Mrs Nixon (republished in paperback under the title Cock-Up); the sexual realist drama Panic, a compassionate examination of the mentality of a child murderer; the experimental Asylum, merging the myths of Oedipus and the Old Testament Fall of Man into a narrative written in a style akin to poetic prose; and his first novel, set mostly in Vienna, An Absurd Affair, which he later felt could be sensibly ignored.

The play is a musical fantasy set in a beach bar run by a bald-headed lesbian "barman" and peopled by whores of various sexes and their clientele, including a transvestite thieving vicar.

John Russell Taylor in his book, The Second Wave: British Drama of the Sixties, remarks “for all the play’s cheery light fantastic [it] contains altogether more truth than is quite comfortable.

Three comedies: The Trial of St George, a satire on British justice when dealing with sexuality, inspired by the Oz Trial; Why Mrs Neustadter Always Loses, a wry monologue by an American divorcee exiled on a Greek island; and Keep It in the Family, a satire concerning a happy incestuous family (which Colin Spencer also directed) appeared between 1972 and 1978 at the Soho Poly.

Interest in his work abroad led to performances of his play The Sphinx Mother, a modern Oedipus, at the Salzburg Festival in 1972, and Lilith, a comedy of surrealist images, at the Schauspielhaus, Vienna in 1979.

His moving account of his affair with the Australian theatre director, John Tasker, Which of Us Two?, was first published by Viking in 1990, and then in a paperback edition by Penguin in 1991.

From early on Colin Spencer's creative instincts were applied to food and cookery, and in 1978 his book Gourmet Cooking for Vegetarians was published.

Colin Spencer had huge fun working alongside Katharine Whitehorn to illustrate her column in the national Sunday newspaper, The Observer, with satirical drawings delineating the public's interpretation of fashion trends.

He has completed oil portraits for a wide range of private customers and collectors, including Carl Winter, Director of the Fitzwilliam Museum, Cambridge; Lady Rawlinson; Diana Hopkinson; Michael Davidson; and Canon Frederic Hood of Pusey House, Oxford.

His work resides in a wide range of private collections amongst those of Melvyn Bragg, Germaine Greer, Derek Grainger, Bob Swash, Diana Athill, Prue Leith and the late Mary Renault and Sir Huw Wheldon.

He was latterly intensely involved in creating paintings which he described as "images of the unknown, paths through conflict, compounds of sex and spirit, mysterious reflections, hints and fading memories which unsettle the darkness."

The themes of his recent paintings are: War, Music, and Sex, the interior life of flowers, the sea bed and how do hills form roots.