[Nitram Draw]

Taking that thought a little further, how about limiting the number of certain facilities on specific colony types. Right now the colony designation doesn't mean much, it mostly just tells the AI what to build.
What if you could only build one of any facility on a planet except the facilities that fit that type of colony. For example you designate a colony a mining colony. The only facilities you could build more than one of were ones that directly provided or improved mining.