Blue dots appear to scintillate.pic.twitter.com/NgPbMWyPN5
You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more
But this model cannot explain why some observers see blue in front of red.
Twitter may be over capacity or experiencing a momentary hiccup. Try again or visit Twitter Status for more information.