Two pigments were and are derived from Rhamnus berries; a yellow and a green. The product of the unripe berries is the Giallo santo (cf. M. P. Merrifield, op cit., I clxiv), known in English by the extraordinary names, "Italian Pink" and "Dutch Pink."(Thompson and Hamilton 43)
That page of Merrifield's text explains,
Giallo santo was a kind of yellow lake, which was made from various plants. It was sometimes prepared from the berries of buckthorn (Merrifield clxiv)
and the result is reinforced by the Pigment Compendium that explains,
various species of the Rhamnacea family give a yellow dye on extraction of the unripe berries (drupes)It seems that the medieval artists more commonly would have probably used the local ochers from the land or orpiment, arsenic sulfide, or one of the lead yellows... but I have buckthorn berries from Saco, that I picked, for free, and don't feel like playing with arsenic or lead today!
Here's a preview picture of them,
|yellow clothlets from green buckthorn berries in the foreground, sap green clothlets behind|