She was involved in the compilation of a controversial planning report, published by An Taisce in 1983, which highlighted abuse of planning laws by city and county councillors across Ireland, and in particular in counties Galway, Mayo, Donegal, Kerry and Louth. She served as Environmental Officer for An Taisce before being elected National Chairman in 1987, the first time a chairman had come from one of the western county associations. She continued to use her position to campaign against misuse of planning laws, for a clamp down on pollution of rivers and lakes, and against a move to scrap An Foras Forbartha, a body that provided independent monitoring of pollution. During her three years as chairman, until May 1990, she was particularly involved in debates over local environmental and planning issues, in particular over gold mining in the west of Ireland, a proposed airport for Clifden, and the planned sewage treatment plant at Mutton Island in Galway. In 1991 plans were announced for a new visitor centre, to be located at Mullaghmore in The Burren. Colleran was among those who were part of an appeal, saying that while the plan for the national park was welcomed by An Taisce, they wanted the visitor centre to be located three or four miles from Mullaghmore. President Mary Robinson appointed seven new members to her Council of State in February 1991, including Colleran. Other new members appointed at the time were Monica Barnes, Patricia O'Donovan, Quintan Oliver, Rosemarie Smith, Dónal Toolan and D. Kenneth Whitaker. The new Council of State represented a wide spectrum of Irish life and was widely welcomed, although Fine Gael was disappointed that its leader John Bruton was not included. In 1991, she was one of 15 people appointed to Taoiseach Charles Haughey's Green 2000 Advisory Group, to determine which problems would face the environment in the next century. The group was led by Dr David Cabot, special advisor on environmental affairs. She was appointed a member of the National Heritage Council in 1995 by the then Minister for Arts, Culture and the Gaeltacht, Michael D. Higgins. In the same year the Minister of State at the Department of the Marine, Eamon Gilmore, appointed her to the chair of the Sea Trout working group to oversee the implementation of recommendations to tackle a decline in sea trout stocks, particularly in the west of Ireland. In 2003 Colleran was elected as member of the Royal Irish Academy. She was recognised at the annual NUI Galway Alumni Awards in 2004 when she received the award for Natural Science, sponsored by Seavite Bodycare Ltd., which acknowledges a graduate who has made an outstanding contribution in the field of natural science.