I thought it was interesting to see the "yellow" states in '48 and '68.
1) In 1948 the staunchly Democratic(Blue) South got angry with Democrats like Truman who formed A Civil Rights Commision to investigate Human Rights abuses against Blacks.
Truman also desegregated the military in 1948 & Northern Democrats like Hubert Humphrey called for an end to Jim Crow & a Civil Rights Act.
The South got pissed & started the DixieCrat party & nominated Strom Thurmond for PRESIDENT. Democratic party backtracked on Civil Rights legislation & the Southern Dixiecrats returned .
2) In 1968 Southhern Democrats got pissed again after Northern Democrats (JFK)finally decided to call for real Civil Rights Legislation,Pass Civil Rights legislation written by Northern Democrat(Emanuel Celler of NY) & signed ironically by a Southern Democratic President(LBJ).
That was the last straw & Southerrn Whites took their ball & left the Democratic Party
The South would have been yellow in 1964, but the Civil Rights act was passed too close to election time (July)for a 3rd party challenge so they held their nose & voted for Barry Goldwater (who actually voted against the Civil Rights Act).
The GOP saw this dissatisfied /Angry Southern White Democrats & played the Southern Strategy & has basically owned the Southern White vote ever since.