Because of how WDR works, it will affect the saturation, especially in the very bright and very dark areas which have less saturation accuracy.
The camera should try to keep the result accurate for both settings, but I don't think Viofo try very hard to get accuracy, they try to make it look good, which means different things to different people. Having different results in the two settings gives people a choice.
Generally I don't recommend using WDR on Viofo cameras, it just gives a different "exposure" setting, which you can choose if you like it, but WDR off normally records slightly better detail. In reality, WDR Off is still using WDR, just less of it. On other cameras WDR on can be the better setting.