here is a short history of Plainview – Old Bethpage John F. Kennedy High School, which color was changed when the name changed in 1991?

The school was opened in 1966 under the name John F. Kennedy High School. It was Plainview's second high school. Originally, all senior high school students went to Plainview High School, but were split by residential location when JFK High School opened. In 1991, Plainview-Old Bethpage High School and John F. Kennedy High School were merged into the John F. Kennedy High School building. The school was renamed Plainview-Old Bethpage John F. Kennedy High School. The newly merged school abandoned Plainview High School's colors of green and white in favor of John F. Kennedy's blue and white. Both the original Plainview High School mascot, the Gulls, and the John F. Kennedy High School mascot, the Eagles, were replaced with a new mascot, The Hawks. It is now the only public high school for residents of the community of Plainview and Old Bethpage.

The school colors swapped out green for blue and white stayed the same.