Registration papers should be proof, but without DNA confirmation one can never be positive. I know a breeder (in another breed) who was getting old and a bit confused and I am sure some of her pups' parents were not accurately attributed, but the pups were purebred, just possibly from different sire. Coat colour can vary tremendously and it's more likely when it isn't a disqualification in the breed. If you are buying a dog described as purebred then there should be registration papers given to you. A DNA test should tell you whether the dog is Basenji or mixed with something else, if you really want to know.
Looks can be so deceiving- here is an article of a woman who adopted a rescue dog in N.J. Dog looks like a basenji - even her vet thought it might be basenji. She did an Embark DNA test - no basenji. Turned out the dog was a mixture of Mountain Cur, Rat Terrier, Beagle, and Boston Terrier. link text
Agree with @elbrant and I'd like to add, when you return be very matter of fact, do not make a big fuss, particularly if she is excited and effusive in her greeting to you. Sure, acknowledge her if you must but don't make any sort of big deal out of it. Go about your business, e.g. if you've been shopping, put your things away before spending any time with her. Your goal is to make your absence just part of a normal routine, nothing to be excited about. I've had two separation anxiety dogs, and you know you have won the battle when the dog just glances at you in an "oh, you're back" way and doesn't bother getting off the couch! Yes, people like it when their dog greets them and makes a big fuss, but if you feed that behaviour you give too much emphasis to your absence and that can grow into anxiety in your dog.