On the top right it tells you the overall colony cost is still 2.00, that is the maximum of any of the other factors listed below that. In this case, 2.0 from having a dangerous atmosphere. If you're looking at older documentation, Carbon Dioxide didn't use to be a dangerous gas, but now in C# it is classed as such. You must remove it. That still leaves the 1.002 Water, but you're already working towards that. Once the planet hits 20% hydrosphere and has the carbon dioxide removed it's colony cost will drop to 0.