If you wire-or the video with text, you'll be able to read the light text on a dark background, but not the other way around. I had to cope with this many years back. You can look at the analog level of the video, and, if it's more than 30% of white, you won't be able to produce legible white text. You can either use a reverse-video font, in which case you'll have a black background that obscures video and shows text only, or you can invert the pixels by pulling them to black and allowing the rest of each character block to float to the video level or an injected white level, the latter also obscuring the video. When the background is between 30% and 70% of white (full brightness), you're in trouble either way.

You need a good way to do this. It's not so simple. Maybe there's a canned solution, but I don't know of one right now.

RE