Hi mardanseb. I'm not a plant expert but have you done a google search on "camellia" - could be the soil isn't right or overwatering. You might want to post your question in Home & Garden, there are loads of plant experts up there. Good luck.
Chlorosis causes yellowing of the leaves as well but that's due to lack of iron !!! but you are right Dot about chlorophyl and sunlight and we are sure showing our ages here - 'o' levels indeed !!
According to my Encyclopedia of garden plants and flowers, it could be frost damage, also make sure it is in a line free soil I will post a photo of my Camellia when it flowers