Slaves, freedmen, and foreigners were not allowed to wear a toga--they would have worn a tunic with a belt (these could be various colors, but white was popular). Tunics either had short sleeves or no sleeves (long sleeves were only for women). Men also sometimes wore cloaks/capes which could be any color. Of course, what color you could use depended somewhat on how much you could afford (more on that here.)
And of course, if you were a Roman Guard, you would have a whole different attire.
If you're wearing a toga over it, a white or t-shirt will do, and of course shorts underneath.
Fitted sheets sort of mimic the rounded look of a real toga.
This video below shows how to wrap a toga (thanks Lauren!).
Roman Men's Hair
According to this video, "Roman hairstyles were similar to today except that they never parted it...they combed it forward from the crown or up from the sides so that it distributed evenly over the top of the head. " Parted hair was only for women. In the late 1st century men went clean shaven and often liked to curl their bangs (as did women) with something like a curling iron.
Most of the info about men's clothing I got from this fascinating site.