Colors in pharmaceutical containers - casual or meaningful?

[Gab19]

They seem somewhat hierarchical in their shapes, so perhaps color is significant.

You just reminded me another thought I had - the way of preservation. That could be also indicative of which plants are depicted in relative recipe. The simple tubular containers in wood for what can be preserved just dry but those elaborated that are probably made of glass or some other material (as was discussed in another discussion here about containers) could preserve what had to be kept in oil or needed to preserve the aroma?

I didn’t find anything about methods of preservation nor anything detailed about pharmacy in Middle Ages. Do you know any article to suggest? Maybe that could be also helpful in identifying plants in recipes.