My stepson bought his 500D in 2012. He says he's done 500k clicks. I say he's done less. His last two home studio sessions have produced photos with a yellow cast. Not severe, and I think it's a lighting issue. He says correct WB was used. My take is that if sensor was failing it would be a severe cast. I can't post pics without his permission so ill just have to ask your opinion as to what could cause it.