Two non-corporeal Kerkhovians who repair Spock and Chapel after a shuttle accident but, misreading his mixed heritage as damage, remove his Vulcan half.
Yellow and Blue are the names given to two Kerkhovians in the second-season Strange New Worlds episode Charades. They are heard rather than seen, represented by coloured light, and the voice is provided by Anjuli Cain.
Spock and Christine Chapel are injured when their shuttle is caught by an anomaly near the moon of Kerkhov. The beings who live there put them back together, taking Chapel as their model, and Spock wakes up entirely human just as he is due to host T'Pring's parents for an important ritual dinner.
Chapel, Uhura and Ortegas fly back to the anomaly to ask for a correction. The Kerkhovians behave like bored officials at a complaints desk and are unmoved until Chapel admits how much Spock matters to her. They then supply the means to restore him.