Green’s Dictionary of Slang

1. (US) corned beef hash.

1897		L.A. Times 9 Apr. 5: ‘Red, white and blue’--corn beef hash.
1968		Orlando Sentinel (FL) 2 May 23/4: Red white and blue is cold salt beef.

2. (US) a plate of mixed flavour ice-cream.

1896		Record Union (Sacramento, CA) 2 July 5/1: The cake and ‘red, white and blue ice cream’ were being served.
1902		N.-Y. Trib. section II 27 July 2: ‘Red, white and blue’ is a plate of mixed ice cream.

3. salt (US: corned) beef.

1972

Hartford Courant (CT) 12 Nov. 4F/4: Gloss. of Cockney Eng. [...] Red, white and blue is cold salt beef.