Looking into the Philly.com (Inquirer) database, I see the word "colonial" appears 1,160 times in 1908; 2,620 times in 1918 and 2309 times in 1928. So you may be onto something. And looking at the word "colonial" at Google Ngram shows a nice peak in 1919, But why then --- do you think?
This is some interesting information. Perhaps both searches would yield even higher results if extended to the Spanish-American war?