Your son Kṛṣṇa appears as an incarnation in every millennium. In the past, He assumed three different colors — white, red and yellow — and now He has appeared in a blackish color. [In another Dvāpara-yuga, He appeared (as Lord Rāmacandra) in the color of śuka, a parrot. All such incarnations have now assembled in Kṛṣṇa.]
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
आसन् वर्णास्त्रयो ह्यस्य गृह्णतोऽनुयुगं तनूः । शुक्लो रक्तस्तथा पीत इदानीं कृष्णतां गतः
āsan varṇāstrayo hyasya gṛhṇato'nuyugaṃ tanūḥ | śuklo raktastathā pīta idānīṃ kṛṣṇatāṃ gataḥ
SB 10.8.13