I was curious myself so did a search. Actually it was earlier.
"The first known film to successfully use the Kinemacolor process was A Visit to the Seaside (1908)."
But they say that process required special equipment. Probably extra time & even extra money to produce.
I haven't watched Gone with the Wind nor Wizard of Oz in a very long time but I believe they did a great job in going from the black & white to the colorized version with what they had to work with.