Principal Feasts are always kept on their day even when an option is provided for either anticipating or transferring an observance of them on a Sunday. While the Book of Common Prayer was very strict about the observance of red letter days on the days themselves, there is now a tendency to move Holy Days to a convenient weekday, if there would not otherwise be a celebration of the eucharist on the day. This practice, now recognized in the BAS Rules of Precedence (page 17), is worth considering in parishes where Holy Days would otherwise go unobserved.
On Principal Feasts and Holy Days, the full propers (both prayers and readings) should be used. No other option is provided. Propers for Principal Feasts and Holy Days will be found either in the BAS, pages 398–431; or in For All the Saints. The liturgical colour of a Principal Feast or Holy Day normally takes precedence over the colour of the season. (An exception might be made for Holy Days in the Easter Season when white/gold might be the preferred choice.)