I've always noticed it is recommended to store stock solution (or any mixed b&w developers) in an amber or opaque storage container. What is the degrading process that occurs when developers are exposed to daylight? Are all developers affected? I need to mix up some Xtol (for replenishment) and am out of the brown storage containers at the moment. Common sense tells me not to play with fire and wait till I can pick up a two 1/2 gallon containers (I have a few 1 Litre bottles for the extra) but I've always wondered about what it is that causes issue.