What do I do if my supervisors at work treat me like I am retarded?

I want to do more things at my job rather than just type when the boss hands me work like I want more responsibilities and do what everyone else does and I AM THE ONLY ONE WHO SITS AROUND LIKE DENNIS THE MENACE WHEN THERE IS NO WORK! And I would even go to my supervisor and say: "You know. I really want to learn more job skills. Is there anything else I can do? I don't like just sitting around and not being productive." and he said: "No I am afraid not. You just do what you do and wait while we give you work." Now I do have a disability of aspergers and its very hard for me to speak up but I am afraid they take advantage of me and not let me do other job responsibilities of what I am capable of and instead I am mainly sitting around and I look extremely unprofessional and weird like a little kid who is visiting their dad at work with just sitting there and my boss even one time GAVE ME A COLORING BOOK TO COLOR WHILE I WAS WAITING!!! And told me to stay out of his way. Why doesn't he just fire me if he doesnt have anything for me to do or just lay me off? He might as well but its weird how he wants me there just to sit around. I feel sad about it too because everyone else is working and I am the only one in the dept who has nothing to do and I don't know what to do about this if I already talked to my boss?