The label bio is always a quite interesting one. On the one hand the label supports bigger cages for animals and thus serves utilitarian purposes. On the other hand it leads to some farming choices for which there no real reason.

The EU commission just discovered that chicken eggs by nature are neither red nor blue and therefore painting them red or blue might violate the bio idea. Therefore the Eu commission is planning to rule that there no such thing as a red bio-egg.

http://deutsche-wirtschafts-nachrichten.de/2014/07/20/eu-kommission-will-faerben-von-ostereiern-verbieten/ (German source)