Wax won't discolor they way soap does. Many vanillas tend to discolor soap but its not the same with wax.
Most discoloring in wax occurs from light. Light that can discolor wax can come from sunlight, ultraviolent, overhead lighting, etc.
Use UV Inhibitor in your wax to help it keep its color. Even if you don't color your wax it can fade or turn from light. Most wax suppliers carry it. Just follow instructions for adding to your wax.
FO can also discolor wax but UVI won't change that type of discoloration. If your wax turned a light tan or cream color from the FO after you blend it into the wax you still want to use UVI to keep the new 'color' consistent or from any new discoloring or fading.
UVI works primarily with blocking ultraviolet light that can discolor or fade wax colors. Whether you use color or not you still want to use UVI to keep your color from changing or fading and to help it stay uniform.