Drosophila are one of the most studied species in the world, offering a great number of answers to complex questions. While a fly fundamentally different in many ways to a mammal, it has proven useful in the past to study flies first because they are easily examined and then to apply to knowledge gained in those studies to mammals. The visual system of flies-that is everything but the actual eye, which is admitted to be fundamentally very different from vertebrates,-is believed be similar between flies and mammals, especially the of the circuitry connecting the retina to the brain. So a publication was put out talking about fly eye targeting to satisfy the curious.
As it turns out, a fly eye starts the process of neuron targeting by sending axons out of retina into a layer of tissue called the lamina. Some of the axons sent into the lamina form a connection to various cells there, which work to process/detect motion. Another set of cells (although some of them have similar labels to the motion detecting cells) send their axons past the lamina to a layer of tissue called the medulla. The medulla is separated into six regions and each of the axon from the retina that has passed the lamina targets one of these specific regions. The axons placed into the medulla are responsible for color processing and work to signal different parts of the fly's brain about color. Both sets of neurons (the ones for motion and color) use hedgehog to locate their exact resting location in the cell. Of course, a handful of other proteins are used too and things become fun.
The actual article is extortionately in depth and would take a paper just as long as the journal article to write about. However, it does give a much more detailed account of the generally too simply and incomplete overview have given. Read up, if you'd like.