From a priest:
I have looked everywhere for an answer to the question of the required (not just proper) color for exposition of the Blessed Sacrament during Lent (and other seasons). I know that the CDW, in Eucharistiae sacramentum, 92, mentions that the benediction is to be done with a white cope and humeral veil, but what about the act of exposing the Sacrament, apart from the rite of Benediction? At the seminary where I teach, I saw the transitional deacon using a purple cope to expose the sacrament. I’m pretty sure this is wrong — I believe he should have worn white. But is there a document I point to so that this can be corrected?