Gresham is a life member of Rainbow Auckland. He became a GABA Charitable Trust (now the Rainbow New Zealand Charitable Trust) Board member in 2008, and in January 2010 was appointed to the role of Chair. In 2011, he chaired the GABA-led Community Consultation process which led directly to the formation of the Auckland Pride Festival Trust in 2012. He was one of the Co-Chairs of Auckland Pride through 2013 its inaugural year relaunching the Pride Festival and Parade.