Concerning bone, like any other natural material, it is susceptible to degradation by UV light.... whether stabilized or not. You simple cannot totally overcome a natural material's characteristics. 

  Stabilizing may slow the bone changing, but it will not totally prevent it.  

  You mentioned "bone and wood"..... I would be more concerned about the movement of each material in the finished product. Natural materials often move at different rates, and combining the wrong materials in a knife handle can cause a variety of failures.  

  There are some natural materials that experienced makers tend to shy away from based on their experiences in knowing the given material will cause problems.  For me, bone is one of those.  Not only does it shrink and expand significantly more then most woods, but the yellowing you spoke of, is next to impossible to stop/overcome.  If you mix the bone with a wood such as Maple, or just about any of the native US hardwoods, there WILL be problems.  

  Sometimes as a Knifemaker, you need to explain to a client that certain things are not a good idea, and if they won't trust your judgement, the best option is to turn down the order... which is what I would do in this case.  I've been down the road of bending over backwards to meet a clients wishes when I knew better, and paid the price in repeated grief, repairs, and even refunds.   Once a knife goes out the door, the worst thing for any knifemaker is to see it again....and again....and again.   Whether that happens or not is up to the individual knifemaker.  😉