COLOR-MODEL settings "3" and "4" are similar to models "1" and "2". The primary difference is in reverse-video, which appears as white-on-gray. Also, background colors are brighter. .
For COLOR-MODEL "3", the foreground and background colors are exchanged for each other, but only if they are both black or white. If either the foreground or background contains a color other than black or white, then nothing happens. This is equivalent to running the monochrome parts of your program in reverse-video while maintaining the color portions unchanged.
For COLOR-MODEL "4", the foreground and background colors are exchanged for each other, but only if the background is black. This mode insures that you never have a black background.
Equivalent settings
COLOR-MODEL "3" is equivalent to Color-Trans "3", Intensity-Flags "34".
COLOR-MODEL "4" is equivalent to Color-Trans "1", Intensity-Flags "34".