If/when it dries, does it leave white sort of crystals? If it's very milky, I might be worried about too much calcium in the diet. Rabbits don't process it well and it can lead to bladder sludge and I think kidney problems too. What sort of hay are you feeding, and what are the pellets you're feeding based on?
Lucernce/alfalfa hays tend to be higher in calcium, and the same with the pellets based on them. Some leafy greens also have higher calcium than others such as silverbeet and I think spinach.
Otherwise, generally rabbit pee can be almost any colour, as what you feed them changes the colour such as carrots etc.