The Yellow Segment of the Universal Collective stood for philosophy, thought and purity. They were the expression of the UNI culture and considered the weakest voice in the Collective as they spoke out against the White Segment. (In mild criticism of course)
It is believed that it was the Yellow Segment that picked the Ker and gave them the gift of Psionics.
Some scholars believe it was the Yellow Uni who also bestowed the gift of Psionic powers upon the Saresii. However, the Saresii reject that theory and believe it was a natural process without external aid.
Latest evidence suggests that the psionic abilities of the Saresii come from a completley different source. (See Chrom )