Read this post about an introduction to the Rasas.
Read this earlier post of mine [Link to post] to understand how Bhishma intervened in the swayamvara of Amba, Ambika and Ambalika and rode away with all three princesses with the intention of getting them married to Vichitravirya.
On learning that Amba was already in love with King Salva, Vichitravirya married Amba and Ambika. However, shortly after his marriage he succumbed to tuberculosis and died before he could beget any heirs with either of his wives.
Dismayed by the fact that Vichitravirya had died without an heir to the throne, Satyavati asked Bhishma to beget the next generation of Kurus through Vichitravirya’s wives, to which he declined citing his vow of remaining celibate for life. As a last option Satyavati instructed Bhishma to summon her son, Veda Vyasa who was born from her union with Sage Parashara.
When Vyasa came to Hastinapura, his mother Satyavati ordered him to go to the beds of Ambika and Ambalika and beget heirs to the Kaurava throne. Now Vyasa had been born with a dark complexion and years of penance and asceticism had taken its toll on his facial features as well which had become extremely rough and dark over the years.
As a result, when Vyasa went to Ambika’s bed, she closed her eyes partly due to Vyasa’s severe countenance and partly due to her own shyness. When Vyasa figured this out, he went and told Satyavati that Ambika’s child would be born blind as she closed her eyes when he went to her bed. The son that was thus born was then called Dhritarashtra.
As a result of this, Satyavati warned Ambalika to remain calm when Vyasa visited her. But despite this warning, Ambalika’s face went completely pale at the sight of Vyasa and thus, the son born of their union, Pandu, would suffer from anemia and would therefore be unable to rule the kingdom.
Thus, the bibhatsa rasa (disgust and aversion) makes an appearance in the Mahabharata in the form of Ambika and Ambalika’s reaction to Veda Vyasa’s face and his overall appearance which resulted in Dhritarashtra being born blind and Pandu being born anemic.