What I have always heard about integrating cats, is that cats are more tuned into smells than visual things. If you take a towel and rub it on Albert, and then put that towel with your other cats, they will get familiar with his scent before you introduce him. Albert has no doubt picked up the scent of your other cats already so the towel trick probably won't make a difference with him He will just need to stay in his "hiding place" till he is ready to come out.