Kathryn Adeline Rainbow was born in 1921 in Wheeling, West Virginia to John Henry and Addaline Holly Rainbow. She attended high school in West Virginia at Lincoln High School, finishing her senior year at Oberlin High School in Ohio. Upon graduation, Rainbow attended Fort Valley State College in Georgia, receiving a B.S. in 1942. She went on to Meharry Medical School in Nashville, Tennessee where she received an M.D. She completed residencies at Harlem Hospital in New York, Mercy-Douglass Hospital and Children's Hospital in Pennsylvania, and Freedman's Hospital in Washington, D.C.

Following the completion of her education, Rainbow started a private practice in Rocky Mount, North Carolina, the hometown of her then husband, Frederic Bryant. She then became staff physician (1954) and later superintendent (1960) of Lakin State Hospital in West Virginia.

Rainbow left West Virginia to attend the Menninger School of Psychiatry in Topeka, Kansas in 1962, completing her studies in 1965 and becoming the first African American female to become a psychiatrist in Topeka, Kansas. Subsequently, she worked at the Topeka State Hospital and, later, the Shawnee Community Mental Health Center (1979). In 1981, Rainbow-Earhart (her name changed in 1966 after her marriage to William Earhart) took a job at the Kansas State Department of Corrections, retiring in 1983.

Dr. Rainbow-Earhart was a member of many organizations, among them the West Virginia Medical Society, the American Medical Association, the Kansas Medical Society, the American Psychiatric Association, the Black Psychiatrists of America, St. John A.M.E. Church of Topeka, Alpha Kappa Alpha, Links, Inc., Quota International, and the NAACP. She also served on the boards of many organizations.

Dr. Rainbow-Earhart married twice and had two boys, Frederic Jr. and Holly, from her first marriage to Frederic Bryant in 1950. She married William Earhart in 1966. Rainbow-Earhart passed away in 2011 at the age of 90 in Topeka, Kansas.