Can you show list with all colors for outline in co-op?
You can search for "hex color picker" and use a hex color (e.g. "#445588") to choose any color.
Named colors are white, black, gray, red, green, blue, aqua, yellow, pink, orange, lime, purple, "night" (distinctive dark blue), and "fab" (neon pink). These come from another mod of mine, Spelunky SD.