Lord Shri Krishna becomes Lord Shri Gauranga from the Varaha Samhita http://www.naam-yoga.com/Govinda-becomes-Gauranga.html
During the rasa-lila, Shrimati Radharani left the dancing arena. Lord Krishna went searching for Shrimati Radhika throughout the groves of Shri Vrindavana Dhama, but He could not find Her due to the nature of His transcendental pastimes.
Sitting under the tamarind tree at Shri Imli-tala, a dear place of Shrimati Radha's, Lord Shri Krishna begin chanting, "Radha, Radha, Radha...". While totally absorbed in thoughts of Shrimati Radharani, Shri Krishna's bluish-black transendental body assumed the radiantly golden color of Shrimati Radhika. At that moment, Shri Radha and Her gopi girlfriends arrived there and became captivated by that golden form of Shri Krishna.
When Shrimati Radharani said, "This is definitely Shri Krishna sitting here", Lord Krishna left His mood of separation and noticed Shrimati Radharani and the gopies. Shrimati Radha then asked Shri Krishna about the meaning of this unprecendented and unparalleledly beautiful form.
"After searching for You thoughout the forest, Shri Krishna replied, "I sat here and began to chant Your Name. Gradually, My body assumed Your effulgent golden color, and I inherited your divine emotions, which enabled Me to experience the intense mood of separation You feel from me. I have never tasted such nectar before. Thus, I desire to taste it again and again. So in Kali Yoga, as Gauranga, I will again accept Your mood and golden complexion and freely distribute My prema bhakti (pure love) to all conditioned souls. And I will eternally relish Your supreme love in the form of Shri Gauranga in My Holy Abodes of Shri Navadvipa Dhama and Shri Jagannatha Puri Dhama."