This is a story about how fillies born (it is always fillies) with pink are corrupted creatures of Discord (by superstition). This is one of the instances where it is true. But whether Pinkie has had a hand in it or whether it's simply due to cultists or ancient cultist bloodlines creating this "genetic defect", it is post war tradition to kill these fillies at birth. Lest they bring ruination to their family.
Most instances of pink fillies are usually in the empire seeing as many ponies have evolved to be born with warm colours. As such red and white coated couples are seen as a taboo in imperial society, for obvious reasons. For this reason Lunar ponies see it as taboo to mate with solar ponies for fear of corrupting the Lunar race as well their natural animosity.
Love between the two races as such is near impossible, not only for political and social reasons, but for religious and genetic reasons too.
Disclaimer: this is a War for Equestria group story. Link is found below for more information on the universe and fanon.
http://www.fimfiction.net/index.php?view=group&group=703