Here's a couple of websites for tams done all one color. You'll probably need a set of dpn's (double pointed needles) when you start your decreases because there won't be enough stitches on your circular needle to stretch around the needle.
http://droppedastitch.blogspot.com/2...weedy-tam.html
http://www.whatifknits.com/?cat=30
Ravelry also has lots of tams on their site. You should check it out.