How is Krishna's role subtly incorporated in "Rasamanjari" by the artist?

As the archetypal lover

Answer: As the archetypal lover
Although Krishna is not explicitly mentioned in the text, painters have introduced him as the archetypal lover.

Bhanu Datta, a Maithil Brahmin who lived in Bihar in the fourteenth century, composed another favourite text of artists, Rasamanjari, interpreted as the ‘Bouquet of Delight’. Written in Sanskrit, the text is a treatise on rasa and deals with the classification of heroes (nayakas) and heroines (nayikas) in accordance with their age — baal, taruna and praudha; physiognomic traits of appearance, such as padmini, chitrini, shankhini, hastini, etc., and emotional states, such as khandita, vasaksajja, abhisarika, utka, etc. Though Krishna is not mentioned in the text, painters have introduced him as the archetypal lover.