A new server-side change has started rolling out bringing us a new “download” badges that perfectly compliment the Material Design changes we've been seeing from the Play Store as of late. The badge shows up for any app that has at least one download and changes colors as they app becomes more popular. Those apps with under 5000 downloads have a gray badge, 10000 to 50000 is blue, 100000 to 500000 is green and anything over a million gets an orange badge.
While this isn't a massive change, it’s still a welcome one for those that are quickly checking out an app to decide if it’s worth the download. Keep in mind you probably don’t need to do anything to get this to show up other than wait for Google to turn it on for you, though you may need to have the most recently released Play Store update (4.9.13).
[Source: Android Authority]