It is possible to get dedicated chip, but you will need much more hardware.
Old CRT monitors have color OSD chip, which is I2C driven (forgot model, but you can find it with ease). The main issue is that it operates with RGB data. So to use it with your video in video out, you will need to "disassemble" your video signal, add OSD and "assemble". The above mentioned maxim chip passes color without problems, I've been using it with PICBASIC (adapted basic stamp code)