Trường Bộ Kinh (Digha Nikaya) 1:611
SUJATOAjjhattaṁ arūpasaññī eko bahiddhā rūpāni passati nīlāni nīlavaṇṇāni nīlanidassanāni nīlanibhāsāni.
Not perceiving form internally, someone sees forms externally that are blue, with blue color and blue appearance.