The recent discussion about colour change of bariopahamacosiderite https://www.mindat.org/forum.php?read,19,373867,406116#msg-406116 remembered me that I observed a colour change from green to brown at self colleted bariopharnacosiderite crystals from Clara Mine, Oberwolfach, Ortenaukreis, Freiburg Region, Baden-Württemberg, Germany also from Point 16.1, Hohenstein, Reichenbach, Lautertal (Odenwald), Bergstraße, Darmstadt, Hesse, Germany and from Monstranzenbaum, Frauenstein quartz vein, Wiesbaden-Frauenstein, Wiesbaden, Hesse, Germany. From the last location I colleted some small bariopharmacosiderite crystals in 1995 which changed in colour from bright green to yellow brown at dark and 30 % humidity within a year. One of the crystals was immersed in water (set to PH <2 (with HCl) at room temperure for 3 days. Its colour changed back to green with a brown core.
See Pictures below.




Crystal size is 0.8 and 0.7 mm.

So there is a reason to repeat the experiment with bariopharmacosiderite from other locations.