Hello!
There are several interpretations of the colors of this stork. For instance in the Osprey books (
Nieuport aces and
GC12 Les Cigognes), this stork is painted red body and blue beak and feathers.
What is sure is the stork is definitely painted with 2 different colors.
The top image of your link shows two different tones on the stork (there are cleaner pictures of N1531 where this is more obvious, there's also a picture of René Dorme's N1720 "père Dorme 3" with the same stork)
Notice the top wing cockade behind Guynemer's legs, the red outer ring is not very dark, the body of the stork is darker (as is the numeral "2", not visible on this photo)
On another hand, it is possible that the factory painted cockade and the unit painted insignia did not use the same shade of red
HTH
Gilles