I would definitely agree that generally speaking the older the material is, the darker the concentrate will be. I think both factors you mention can impact the resulting product. In my experience coordinating concentrate processing in the Colorado legal market for the last few years, if you run some material with butane and some material with propane generally butane will produce a range of more pale beige to dark brown coloration while propane will generally produce a brighter, lighter, yellower in color.

Most labs these days are using a blend of both propane and butane, as Binske does. As I understand it, that allows the aesthetic appeal of the propane production, while maintaining a high potency level, desired consistency, and terpene content.