This script is a simple helper for finding the right numbers for a prim and face in a linkset you are interested in.
Simply set the color of the face to something you will recognise. eg black when all the others are white, then drop this script into the contents tab of the prim. It will produce a report then delete itself.
[16:30] Object: Prim 2's colors are:
0 : <1.00000, 1.00000, 1.00000>
1 : <1.00000, 1.00000, 1.00000>
2 : <1.00000, 1.00000, 1.00000>
3 : <1.00000, 1.00000, 1.00000>
4 : <0.00000, 0.00000, 0.00000>
5 : <1.00000, 1.00000, 1.00000>
So in this example prim 2, face 4 is the one that I wanted

CODE
// DD Face Color Reporter
// by Domino Marama
default
{
state_entry()
{
integer sides = llGetNumberOfSides();
string msg = "";
while (sides > 0)
{
--sides;
msg = (string)sides + " : " + (string)llGetColor(sides) + "\n" + msg;
}
llOwnerSay("Prim " + (string)llGetLinkNumber() + "'s colors are:\n" + msg);
llRemoveInventory("DD Face Color Reporter");
}
}
Remember to change the llRemoveInventoryLine to match the name you save the script as.