This code works fine for me, using GetDefaultFont rather than GetFont. First thing to check is that sansFont is a valid font. Possibly you have the wrong name for the font in your GetFont call. Also, the color value you're using is strange -- it is only 6 digits long rather than 8, so the red value is zero and the alpha is F6. I'm not sure if that's what you intended. There's also a bug in either your HextToInteger3 function or the call to it, since it doesn't account for the # at the start of the string (it ends up parsing the string "0#F6F6F6"). Unless you're not showing your actual code, there's no reason to say HexToInteger3("#F6F6F6") rather than the simpler and faster &hF6F6F6. Finally, you should almost always use a double buffered roScreen to avoid image tearing, which means you should use SwapBuffers not Finish.
--Mark