During his time as Hodgkins fellow he became friends with former Fellowship recipient Ralph Hotere, who became Parker's unofficial artistic mentor. Parker later honoured his late friend with the massive 2016 work Plain Song for Ralph (the Hotere canvas), which was painted on canvas which had previously been owned by Hotere. Hotere's art influenced Parker's, though Parker's paintings were aimed more at evoking an "emotional response from the viewer, rather than conveying a message".[1]
Parker's work progressed from photographs and drawings to oil pastels, before he began working in oil paint on large canvases, the medium for which he is best known. His key works are large-scale colour field abstracts inspired by the Marlborough landscape that surrounds Blenheim. His most well-known series of works was the extended Plain Song series, which he worked on from the 1980s until his death. These works were an attempt to express the colours of the Marlborough landscape in musical terms, "creating a symphonic tone poem in paint [...], with bold, heavily impastoed canvases which nevertheless have both subtle delicacy and a rigorous use of geometry".[4]