Apparently this choice led subsequent casting directors to assume that the pussycat's ethnicity had to be different from the owl's - and so we see productions that opened not long after the November 1964 world premiere in New York (almost 50 years ago!) also had multi-racial casting.
Eartha Kitt played the Doris role with somebody named Russell Nype in 1966. Nype is still alive although he's 90 years old according to Wiki. Kitt died six years ago at the age of 81.
TOATP was really quite popular even before it was a movie with Barbra Streisand - obviously the movie version dropped the inter-racial aspect - and of all people, Robert Reed played the owl in the 1966 production in Philadelphia, along with somebody named Pat Suzuki - who is also alive and 83 years old.
Of course you know who Robert Reed is - he played the father on The Brady Bunch. He died in 1992 at the age of 59 - he was HIV positive at the time. Reed was gay but deeply closeted.
It's easy to see why it's a popular play - it has a solid storyline, comedy and a prostitute. And most important, only two characters, so it's pretty inexpensive to produce.The movie version has other differences from those early productions of the play besides its pussycat being Caucasian - the play is set in San Francisco, the movie in NYC, the movie has several other characters including a friend of Doris, a friend of Felix and Felix's fiancee and future in-laws. And in the movie Doris turns out to be a porno actress in "Cycle Sluts" which Felix watches, in an hysterical scene where we don't see the movie but hear the dialog, which you can watch here - the entire movie is available free on Youtube.
The play of course has very little to do with the original poem by Edward Lear, except for using the animals to suggest character traits. In fact a selling point for the movie was the big difference - the advertising campaign proclaimed: "The Owl and the Pussycat is no longer a story (sic) for children."
The poem begins: The Owl and the Pussy-cat went to sea - In a beautiful pea-green boat.
Fun fact: although neither the play nor the movie has the two protagonists on a boat, my play JULIA & BUDDY, which freely admits that TOATP is its inspiration, is set on a boat in the second act.
Other fun fact - I just realized this similarity to the original poem last night.