All of my rabbits get fed the same variety of foods, and they have various colored urine. Some is yellow, some is orange... I haven't conducted a scientific study to see if it varies at different times of day, etc., but I would think that if the color was related to feeds consumed they would be pretty consistent as a herd, and that doesn't seem to be the case. It would be interesting to test the ph and mineral content of the different colors to see what exactly is being excreted, but as long as they are all healthy and happy it isn't on the top of my to-do list!