There are many factors, but the film used or the image sensor in the camera has a lot to do with it. Many very nice purples tend to photograph as red. The "purpliest" daylily I ever saw was Moldovan's Concord Town, growing in moist shade at John Benz's garden many years ago. I've been trying to locate a piece of it ever since.
People's perception of "purple" varies though. Most of the time when someone shows me a purple, I see a violet flower.
