I am currently working on adding color to my newbrain modular computer. Currently only the text screen is supported but hopefully it will also support the Narrow Low Resolution graphics screen (256X240 resolution).
Technical info
I am using an extra 32K(4 pages) to save the color info. I added a new command to Basic “OS Col <f>,<b>” that sets the foreground and background color. it supports 16 colors so 4 bits for the fore and 4 for the background. I also intercepted all the function that writes to the screen and redirected them to my ROM at $8000 which on the real Newbrain is empty. So you just set the colors and every time you print or put characters to the screen it automatically saves them to the new color buffer issuing an out command to the screen device.
I have to intercept some more functions so when the screen scrolls the color buffer will scroll too :).
There is a lot of work to be done also on for the grphics support and after the ROM is complete i will change the FPGA which produces the Newbrain screen to support the color.
if you want to know more about my modular computer you click here for the hardware or here for a demo video.