[deather]

Better use,

Код:

public OnGameModeInit()
{
ShowPlayerMarkers(0);
}

Fore more info,
ShowPlayerMarkers

And actually yours would have worked if you had done it this way,

Код:

public OnPlayerConnect(playerid)
{
SetPlayerColor(playerid, White);
for(new All = 0; All < MAX_PLAYERS; All++)
{
SetPlayerMarkerForPlayer(playerid, All, 0xFFFFFF00);
}
return 0;
}