Casper's a dirty boy! Can anyone help????

I have noticed that things rub off on them very easily...Pomegranite, wet toys, etc.... It could be something in the cage, one of the perches maybe? I have noticed that manzanita does rub off on them with a brownish dirty tint. I have noticed that Boo will clean himself (it takes a couple days to notice a difference) and I would just make sure everyone washes their hands before petting. I have heard of shampoos but have never used one as I am not sure how I feel about putting stuff on their feathers other than water. I had a purple bird for a week after the pomegranite "experiment" but he had fun!

Ok living on a farm I guess we are a little dirty lol. Casper being a white bird for the most part has gotten dirty. He showers twice a week for the dust which actually hasn't gotten too bad yet and I think it's cause he's still young. But his white feathers are dirty and mainly where I think we pet him the most. The top of the head, shoulders, and even though we don't pet his tail feathers they are dirty as well. Does anyone have any suggestions on how to get my dirty boy clean?? Thank you!!