I am thinking she may just be too obese to lay. This hen is huge. Quailzilla in my books.
As for light and temperature. My house is always warm so I doubt she is too cold, too hot I could believe at times if I forget to turn down the woodstove(+40C has happened, which is like 102F or something i think). As for light, I would have to take my overhead light apart to check(one of those glass encased things which are screwed into the ceiling with 3 bulbs in it) I think there are 25 watt bulbs in there, not sure...
At least i am not the only stumped one.
The breeder the line comes from has not noted any difference in laying with the colour.
Anna