The choice of comedian Stephen Colbert as the replacement for David Letterman ignited a battle of words online Thursday: While little doubt exists that Mr. Colbert is as funny, clever, charming, and goofy as Mr. Letterman, some media voices loudly complained that the decision by CBS now means that network late-night television will largely remain the domain of white male hosts. When Letterman announced last week that he will step down from the “Late Show” in 2015, television critics immediately started pooling names of possible replacements: comedians W. Kamau Bell, Ellen DeGeneres, Tina Fey, Chelsea Handler, Tig Notaro, Amy Poehler,...