In 1972, Colbourne co-founded, together with Michael Irving and Guy Sprung, the Half Moon Theatre near Aldgate, east London.
He performed in many productions at Half Moon Theatre, including In the Jungle of the Cities, Will Wat, If Not, What Will?, Heroes of the Iceberg Hotel, Sawdust Caesar, Dan Dare and Chaste Maid in Cheapside.
He played Charles Marston, the love interest of Lady Fogarty, in the seventh series of The Onedin Line screened from 22 July to 23 September 1979.
He played the character Jack Coker in the BBC's television miniseries adaptation of John Wyndham's The Day of the Triffids (1981).
During a break in filming of the fifth series, he died aged 49 from a heart attack while renovating a holiday home in Dinan, Brittany, France.