I totally missed this.

-Colonizers have no escalating resource costs.

-Mods the Random Map Generator to spawn Colonizer Blockers, Ruins, and Towers.

-Colonizer Blockers are invisible buildings that prevent colonization.

-Ruins occupy the center of sectors without Colonizer Blockers. They come in three different levels (Bronze, Silver, and Gold) and they can have Marauder or NPC faction defenders. You must defeat them to colonize that sector.

-Towers grant bonuses to colonist efficiency +1/+2/+4 for Bronze/Silver/Gold and they spawn with the corresponding level of ruin.

To be clear, that is for the base mod, the expansion versions add support to the new factions so they spawn with a Silver Tower on their starting sector.

Thanks a bunch for clearing that up for us :D