stock RemoveUnderScore(playerid)
{
    new name[MAX_PLAYER_NAME];
    GetPlayerName(playerid,name,sizeof(name));
    for(new i = 0; i < MAX_PLAYER_NAME; i++)
    {
        if(name[i] == '_') name[i] = ' ';
    }
    return name;
}

public OnPlayerText(playerid,text[])
{
    new string[128];
    format(string,sizeof(string),"%s: %s",RemoveUnderScore(playerid),text);
    SendClientMessageToAll(color,string);
    return 0;
}