VGA VHDL Project

I need VHDL code written for a Nexys2 Board from Digilent, Inc. that focus only on the refresh rate of the VGA Monitor displaying in the color black and White. Each color should be connected to a switch so I can test good and bad refresh rates for each separate color on the monitor. I will need the syntax written for the UCF file to correctly connect to the Nexys2 board to perform testing of the code. I will need instructions on how to manually change the refresh rates in the code myself so I can use Xilinx ISE Design Suite 13.1 to generate a bit file that will be loaded to the board with Adept Software. I need to be able to set good and very bad refresh rates to record for my research for each color.