Since when? I could do it in 2.1, in a federation war.Using the colossus has very specific requirements to be used;
"A Colossus cannot always be used in any form of war. There are certain limitations in which a Colossus can be used. One of them being, is that they can only be utilized in war initiated by a Total War casus belli. Additionally, you can only utilize the Colossus for as long you are either the Attacking or Defending player in a war. If you are engaged into a war that wasn't initiated by or to you (For example, by the means of a Federation, or a Defensive pact), the Colossus will be unable to disable/destroy planets."
Since when? I could do it in 2.1, in a federation war.
Using the colossus has very specific requirements to be used;
"A Colossus cannot always be used in any form of war. There are certain limitations in which a Colossus can be used. One of them being, is that they can only be utilized in war initiated by a Total War casus belli. Additionally, you can only utilize the Colossus for as long you are either the Attacking or Defending player in a war. If you are engaged into a war that wasn't initiated by or to you (For example, by the means of a Federation, or a Defensive pact), the Colossus will be unable to disable/destroy planets."
So, here is the thing that happened:
1) War in heaven started and I became neutral in war
2) I waited and built for about 10-15 years
3) I declared war on one of the awakened empires
4) Used colossus for all of their planets successfully
5) Failed to pacify ecumenopolis that is also their capital (thus this image)