Color is a command used to control how much color you want the game to provide to you, for instance having text indicating you're taking damage colored red. As it's rare these days for players to use slow speed dial-up modems, most players use 'color complete'.
In Game Description
Syntax: color <off, sparse, normal, complete> If you have a color-capable terminal it is possible to turn on color coding. This will highlight objects, mobs, room names, and players in separate colors depending on the color level you choose. Note that the use of color will slightly slow down the transmission, so the use of color is not recommended at low modem speeds. Color off will disable all color. Examples: > color off > color sparse > color normal > color complete