Many American cities are being gentrified — and getting Whiter. Today on “Post Reports,” we go to Denver to see how the city has changed and what longtime residents are doing about it.Read more:As the United States is getting more diverse, the opposite has been happening in American cities over the past decade. In some cities, local governments have invested more money in public infrastructure such as parks and transportation to attract residents as developers have built new upscale apartment buildings. Based on an analysis of census data by The Post, Marissa Lang and her colleagues took a closer look at four U.S. cities to understand the different ways that gentrification is changing life for residents.One of these cities was Denver, where Marissa spent time with politicians and residents who are fighting to prevent displacement and heard about what it’s been like to see their city change rapidly in shape and demographics.    Don’t miss a chance to experience “Post Reports” live! “Post Reports” senior host Martine Powers will be in conversation with author Curtis Sittenfeld at Sixth & I in D.C. at 7 p.m. on April 13. Get tickets here.