Indeed you can, although they are strange and silly. What controls the type of flare is the specularity channels. Coloring them with a material, int the spec but not in any diffuse or bump or ambience, nor transparency, will create all kinds of weird effects. Lights in the scene will make weird colors and shapes, although I've not experimented with this technique enough to make a set of mats corresponding to REAL lens flares. Such as 35mm, 73mm, ANamorphic, blah blah... Here's a sample....