[Benjo]

This one should work properly, and does not require the use of any additional plugins/includes (even though the ones used in Retardedwolf's solution are very useful ):

pawn Код:

public OnPlayerCommandText(playerid, cmdtext[])
{
    if (strcmp("/blue", cmdtext, true, 5) == 0)
    {
        SendClientMessageToAll(0xDEEE20FF, "|_List of blue players_|");
        for(new i=0; i<MAX_PLAYERS; i++)
        {
            if(GetPlayerColor(i) == 0x00137FAA) //0x00137FFAA = Blue color
            {
                new names[MAX_PLAYER_NAME], string[44];
                GetPlayerName(i, names, sizeof(names));
                format(string, sizeof(string), "%s(%d)",names ,playerid);
                SendClientMessage(playerid, 0x7F0037AA, string);
            }
        }
        return 1;
    }
    return 0;
}