I think you want to evaluate the QTY on the screen of the shipment and compare it to the value in the sales order table.  Try

[M:SDH1]QTY(NBLIG-1)<>[F:SOQ]QTY.  Not sure if you want sale qty or stock qty (if you are using different units).  Hope this gets you closer to your answer!

This only seems to work against the FIRST line on the delivery. So if line 1 has a shortage and line 2 does not, we're good. But if line 2 has a shortage, the conditional style doesn't appear.

I have been using X3 for 12 years and I still do not understand when to use what type of "line" reference.  For me - it is a trial and error game.  Try - [M:SDH1]QTY(nolign-1)<>[F:SOQ]QTY.  This seemed to work for me after I saved the delivery.  I was hoping it would change as soon as I changed the qty......  Good luck!

OK, I aborted my complex conditions and am just trying something basic to make sure I understand how it works. So, on the SOH4 (Sales Order Lines) grid  for status is not closed. I want the Pending lines to be red and the Closed lines to be normal black. As you can see, it turns the first line red regardless of the status, and doesn't turn any subsequent lines red. I have tried (NBLIG-1) and (nolign-1) and they both have the same result. Any other ideas?

I feel like I am no help to you!!!!  Other ways I tried something like this is using (indice) instead of (nblig-1).  You could also try no line reference as you are not trying to associate to another line from another table. It should be as you stated - "simple".  Just remember to validate your sales order entry transaction after you make a change to verify it picked up the change.