If you ever have any doubt to whether pictures have been doctored or not, just ask politely. You don't need to use the term "doctored", you could say edited or enhanced or corrected. Any reputable breeder will be polite and honest back, and if they take offense just say their animals looked so beautiful and vibrant you couldn't believe they were real. If they're still offended then maybe it's not someone you want to deal with. Most people should understand you're just doing your homework and making sure you don't get scammed. Many times you are paying for color and doctored pictures are a major offense IMO.
The yellows seem a little oversaturated to me, but that could be caused by many things besides image editing software. Lighting, camera exposure and color settings, monitor color settings all could have an effect. I don't think anyone has enough evidence to prove either way. That includes the people saying definitively that they are not doctored.