Color Modem Chess is the first game for the Coco designed to be used with 2 Coco's hooked up together (either via a NUL modem cable or over phone lines via modems. The game is mostly written in Extended BASIC (and can fit in 16K RAM on a cassette based system; it requires 32K if on disk) with 2 ML subroutines to handle serial port communication in each direction.The players take a turn and select a message to send, and includes audio alerts to the receiving end to the let the player know when the other player has sent a move. The game can be controlled by either joystick or keyboard commands, and you can change color sets to your preference (both options shown above).
I do not have the instruction manual for it unfortunately, but I do know that the J key toggles joystick controls on/off, N starts a new game, M is used to move your piece (once to select the piece to move, the 2nd M to pick the square to move to). It does appear to have some error trapping for when a modem transmission didn't work. The BASIC code even has a few REM statements for certain routines: Retransmit, Change Piece, Get Phone, Resign, Check, Checkmate and Exchange Piece.
Title: Color Modem Chess
Author: Larry F. Perry
Publisher: Double Density Software
Released: November 1982
Requires: 2 x Color Computer 1,2 or 3, 16K RAM (cassette) or 32K RAM (disk), Extended BASIC, joystick optional, NUL modem cable or two modems