Thanks a lot for playing and the feedback! I think there might be some confusion how colonization works. You can colonize planets outside of your network, but the colonization cost will be equal to the distance from the planet to your network. The UI is doing bad job at visualizing this fact if you don't have enough resources to colonize the planet. This will be fixed in the 0.6.0 update, which contains a redesign of the whole "selected unit" panel.
I'll think about removing the terraforming techs from Yimono. They're not completely useless as terraforming can still be beneficial in order to prevent others colonizing your planets in a dire situation or to change the upkeep of your planets. However it's probably not worth researching them just for this utility. There are more features planned regarding terraforming which will make terraforming more useful for Yimono as well, but they will not be coming in the 0.6.0 update yet.