I have to make 2 graduation caps. One as a topper and the other as a cake.
For the topper: It is black. I can't seem to get a good black in just gumpaste. I am struggling on getting fondant or fon/GP mix(for the top of the hat) to get hard enough to hold shape. Any suggestions ?

I used a thin piece of foam core. I used piping gel to "glue" a square of fondant (mixed with tylose) onto the bottom of the foam core. When it set up, I covered the top and edges with another piece of foam core. It held up very well. Here's the finished product:

http://www.flickr.com/photos/hjscakes/4672412267/in/photostream

i see a lot of people using foam core on here. Where can I find that?
I saw your pic of the cowboy boot cake. That is so cute! How did you do the boots?

It takes a lot of black coloring I like to mix cocoa in then add my liquid black color I also prefer to use fondant with gumtex (8 oz fon / 1 tsp. gum) it doesn't dry out as quick giving more time to work. You do have to make a day or two ahead.

I get foam core at Hobby Lobby. Some Dollar Tree stores have the thin foam core, and that would work for the hat.
The cowboy boot pattern came from the template gallery here on CC. Here's the link:

http://cakecentral.com/gallery/1356882

And thank you for the compliment on my cake!

I buy my fondant already tinted black and I add a lot of tylose to get it to maintain it's shape. I did a graduation hat as a topper before and I used a styrofoam egg sliced in half as the bottom part. That way, the grad can keep it afterwards.