I don’t have much time to write this weekends, so here are two recipes for food colour – blue and white – that can stand without much commentary:
141 If you would prepare coloured foods, be it purees or fritters, prepare the colour with wine or vinegar. Blue colour (is made) from cornflowers, dry them in a mortar and pound them very small. Then mix them with vinegar or wine and leave them to steep, or keep them as long as you please. Also prepare green colour this way from (parsley) juice etc.
142 If you would prepare white (colour), heat (pren) eggshells in a pot filled with eggshells, and heat them in a brick kiln or a lime kiln or with a potter. Grind this to dust and then mix the dust with egg whites, thus it will be white, or mix it with vinegar etc.
There is not much to add here, other than that both cornflower blue and eggshell white are more than figures of speech. The former can be used to dye liquid foods like porridges or jellies. I suspect the latter is not really suitable for that, but would work well actually painting foods, something that people did in medieval kitchens of the upper class. It would certainly be preferable to lead acetate and likely less gritty than chalk at least. Eggshells are still used in traditional painting.
The Innsbrucker Rezeptbuch is a manuscript recipe collection from a South German/Austrian context. It dates to the mid-fifteenth century and survives as part of a set of medical and culinary texts bound together. The editor Doris Aichholzer published it together with two related manuscripts and drew attention to the less elaborate, more practical recipes. The manuscript is of unknown provenance, but has been owned by the Habsburg emperors since at least the early sixteenth century. It is now held at the Nationalbibliothek in Vienna. An edition, German translation and commentary can be found in Doris Aichholzer: Wildu machen ayn guet essen… Drei mittelhochdeutsche Kochbücher, Peter Lang Verlag Berne et al. 1999