TRS2006CCG, pg 108 says:
font: The name of the font, default Arial. Other fonts are not functional at this time.
fontsize: The size of the sign text.
fontcolor: The colour of the sign text in r.g.b.
So you're stuck with Arial. For colors you can open the MS Paint program, select Edit/Edit Colors/Define Curstom Colors and then use your mouse pointer to move the indicator in the rainbow colored square and the narrow strip to the right to get the color you want, then write down the rgb numbers.
Bob