Srimad Bhagavatam Canto 10, Chapter 13, Text 46

SB 10.13.46

tavat sarve vatsa-palah
pasyato ’jasya tat-ksanat
vyadrsyanta ghana-syamah
pita-kauseya-vasasah
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Then, while Lord Brahma looked on, all the calves and the boys tending them immediately appeared to have complexions the color of bluish rainclouds and to be dressed in yellow silken garments.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
While Brahma was contemplating, all the calves and cowherd boys immediately transformed into visnu-murtis, having bluish complexions and wearing yellow garments. Brahma was contemplating his own power and the immense, unlimited power of Krsna, but before he could come to a conclusion, he saw this immediate transformation.
 
Srimad Bhagavatam Canto 10, Chapter 13, Text 45
Srimad Bhagavatam Canto 10, Chapter 13, Text 47- 48