Sounds like it could be Space Pirate Captain Harlock
In the future, mankind has discovered a way to travel faster than light and has built colonies on thousands of planets. With humanity fading and the resources of the universe starting to dwindle, some five hundred billion humans began the long journey back home, to Earth. However, humanity has outgrown its capacity to repatriate that many people and thus began the "Homecoming War;" where the many factions of humanity battled for a stake on Earth. The war was long and bloody. It did not subside until an authoritarian universal government by the name of the Gaia Sanction declares Earth a sacred planet, and thus forbidden for humanity to repopulate.
The dark matter was uncontrollable and it decimated the Earth and life was no longer sustainable.
At Harlock's cell, Yama reveals what he had found on Earth. The flower meant that Earth is trying to recover on its own and it might be the "starting over" that Harlock wanted. Emotionally touched at the significance of this miraculous find, Harlock believes he's found his "freedom". Harlock intends to expose the truth of Earth and escapes with the Arcadia.
Here is an image of the purple Earth: