It depends on the species, 3 years can be average for some and in which case, it may just be approaching the end. 3 years for others is a very early time to be kicking the bucket and would be an indication that something is wrong.
The change in coloration makes me think something has gone wrong in your water parameters. I'd suggest doing a full test on your water (hardness, pH, nitrates/nitrites, alkalinity, heavy metals, chlorine/chloramine, etc).
The loss of limbs can be normal from molting, fighting, getting stuck or shedding a limb due to injury. But it can, too, be a sign that there's something wrong with the water or of contracted illness.