An unhealthy design
This was probably nothing but an unfortunate mistake. The designer of these curtains probably figured that yellow is a beautiful color, and white goes with everything, so there’s no reason why they wouldn’t look good combined. It could be a good combination in theory, but the execution is quite unfortunate.
This looks like an unhealthy choice of design – looking at these curtains all day could be quite depressing. Taste might be subjective (is the phrase “De gustibus non est disputandum” ringing any bells?) but this isn’t just a matter of taste, it’s a matter of common sense.