Digha Nikaya 1:613
SUJATOEvameva ajjhattaṁ arūpasaññī eko bahiddhā rūpāni passati nīlāni nīlavaṇṇāni nīlanidassanāni nīlanibhāsāni.
In the same way, not perceiving form internally, someone sees forms externally, blue, with blue color and blue appearance.