The yello cello is a sign that the cigars have been in there a while. I notice this more on traditional cheapo closeouts that did not move and sat in a warehouse. Your question about whether they can make the cello appear yellow is interesting. Now that this is becoming an issue with buyers, maybe the factories will start doing this as a way to move cigars. I would much rather depend on a box date or some other evidence of aging, but the taste never lies; and some cigars do not get better no matter how much time you give them.