It’s blue
1.xxxiii. Item a blue spoon dish (muß) make thus from almonds and of rice. Pound cornflowers well with water, press them through a cloth and keep that. Pound almonds in the same water and force it through the cloth again, so you have blue milk. Make a spoon dish (muß) of rice with that, or a wheaten spoon dish.
If you wish, strew small raisins on it. And do not oversalt it and do not let it burn. These spoon dishes set very well in new pewter dishes or in small white (i.e. freshly turned) wooden bowls.
Cornflower (centaurea cyanus) is mentioned as a colouring agent several times. Here, we actually learn how it is used. The result is still likely to be fairly dull.
My current project are recipes from the Nuremberg Kuchenmaistrey produced around 1490. This was the earliest printed cookbook in German (and only missed being the earliest printed cookbook in any language by a few years). The Kuchenmaistrey (mastery of the kitchen) gave rise to a vibrant culture of amended and expanded manuscript copies as well as reprints spanning almost a century. The recipes seem designed to appeal to a wealthy, literate and cosmopolitan clientele.