Over time the microbes get sadder. If they happen to bump into microbe it likes (the eyes determine which color they like) it will get happier. The microbe it self will pick a target, and only that target will make it happy. The joy is fleeting, only the first bump with that other microbe will have any effect. If they get happy enough they reach nirvana and make the microbes around them a little bit happier while moving to a different plane of existence.