'Albam Exorna' ('Adorn the White') is the motto on the arms of St. Dunstan's College, an English Pubic (Private) School in Catford, SE London. The arms depict in the top left corner an image of the tenth century Bishop, Saint Dunstan. The rest of the shield is white (albam). The point of the motto is that pupils should 'adorn the white' (the undecorated part of the shield) by adding achievements of their own. The school has done its part, now it is up to them to do the rest by realizing their potential. The emphasis is therefore on future achievements, not old tradition. Also individual choice (adorn the white in a way that befits you).
In my humble opinion (full disclosure: I am an 'OD', Old Dunstonian), this is a splendid motto. Yes, it has precedents in Malory and Patrick Hume's 1695 annotations to Milton's Paradise Lost, but it is still a superb motto. Whoever thought it up has more than adorned their white. Even Hogwarts could be proud of a motto like this.