I don't know a lot about color changing daylilies, but I've read and seen a lot of information on how cameras adjust colors in a picture depending on lighting conditions (because I really want to take pictures that show my purple daylilies the color I see them.)
Do you have any more pictures of this plant's blooms from a day when the weather was more consistent? I don't doubt at all that your bloom is changing colors, but the problem with these two particular pictures is the first picture was taken in the overcast (raindrops on the bloom). It had clearly turned sunny for the 2nd picture.
This means we can't say for sure if the color change we see is because of the bloom, or it's because of a white balance effect cameras do.
When it's shady or overcast, a lot of cameras will put a slight blue cast over the image to help your brain see the image as if it were overcast, and on sunny days (or indoor pictures), they tend to put a yellow cast over the picture.
So, can you show us a different day?
I think so many environmental factors effect daylilies in many different ways. Moisture , nutritents, humidity, temperature even winds drying effect. Would these do this in a greenhouse situation? I use worm casting as a fertilizer and part of their clam is they help with deeper ,brighter flower color. I think that my be true. As far as color changers don't know what to expect? Interesting that it is constant. Thanks for your post. 
