In his boyhood he was very fond of horses, made horses of clay and painted them. Therefore he is (sometimes) called Chitrashva (i.e. one who paints horses)
बालस्याश्वाः प्रियाश्चास्य करोत्यश्वांश्च मृन्मयान्। चित्रेऽपि विलिखत्यश्वांश्चित्राश्व इति चोच्यते॥