Here is an interesting project coming out of a Cornell University Engineering class.
Two students tackled the challenge of generating color NTSC signals using the DE2 FPGA development board. What’s interesting is they used the 10 bit VGA DAC to generate multiple NTSC signals.
They were able to re-purpose the Analog Devices ADV7123 Video DAC to generate color NTSC signals. Full source code is included so take a look at this novel solution to NTSC video generation.