WB in the spirit of keeping up, let me help you keep up with me

F.A.Rs = These are the same for every airline
Company policy = These are up to each part 121 carrier

So if this particular carrier has adopted any window shade policy then the fA can enforce it,

(I do not know of any carrier that has a window shade policy for inflight operations purposes) but that does not mean that there might not be one out there that does. Some reasons a carrier might adopt such policies for example: The viewing of inflight movie, Long haul flight that travel through several time zones

The best thing would be check with your carrier then you would be able to say "bull"