Drew, you are correct. Armored infantry regiments were originally called Schuetzen-Regimenter. In Panzer divisions they wore standard field grey field blouses with pink waffenfarbe, and an "S" device on the shoulder strap above the unit number. Panzergrenadier regiments were formed on July 5, 1942 when all Schuetzen regiments were renamed. They adopted a new waffenfarbe- "Weisengruen" (meadow green). This is the light green color. For much of this research and what follows, I am indebted to our unit Haptfeldwebel, Noah Tietze, who uncovered this stuff during the never-ending research we put into our portrayal. Noah located a German OKW Document titled "Truppenkennzeichen Schulterklappen Heer (Gem. „Grundlegenden Befehl Nr. 21" AHA Stab IB (Bekl) 21 – September 1944)." This is the offical decree of what was supposed to be worn by all units. This document lists as following (edited for comparison):
Die Schulterklappen der Uniformen des Heeres tragen
- eine Umrandung in der Waffenfarbe
- die Nummer des Truppenteils (Ausnahmen siehe unten)
- in vielen Fällen Buchstaben oder Zeichen, welche die Truppengattung erkennen lassen
A) Waffenfarben: (Einzelheiten unter B 3.2.)
- WEISS Infanterie-Truppe
- WIESENGRÜN Schützen-Rgt., Panzer-Gren.Rgt
3.2. arabische Nummer, dazu Waffenfarbe:
- WEISS Infanterie-, Grenadier-, Füsilier-Rgt., Inf. Btl (z.b.V.)
Infanterie-Rgt (mot), Grenadier-, Füsilier-Rgt (mot)
Füsilier-Btl ohne Kavallerietradition
- WIESENGRÜN Schützen-Rgt., Kavallerie-Schützen-Rgt, Panzer-Gren.Rgt
So as you can see, Grenadier-Regimenter (mot) wore white piping. What piping was worn was determined not by the Division, but by the unit within the division.
Generally speaking, all soldiers with late-war impressions should wear generic litzen as these were the litzen applied at the factory when the field blouse was made starting in 1938. However, some soldiers liked the look of early insignia and would replace the factory applied insignia with early stuff when they could get it. This was of course the exception to the rule. Mostly this practice was done by long-serving NCOs who still had early stuff. Early tunics that were being reissued were reissued with wartime generic litzen, it is very common in period pictures to see M36 tunics worn with final pattern generic litzen sewn directly to the collar. For soldiers in Panzergrenadier units, using early insignia was not an option because Panzergrenadier litzen never existed, if they had leftover early insignia it would have been the pink piped stuff used in Schuetzen units. In December 1944 all motorized Grenadier regiments were renamed Panzergrenadier regiments but at that late point in the war I would assume that insignia changes were not a priority, though certainly some units would have been issued new boards and some officers would have had the opportunity to get new insignia as well. I believe that it was this edict that created all the Panzergrenadier M44 boards on the collector market today.
Just to make matters a bit more confusing, there did exist litzen for enlisted Schutzpolizei uniforms that had all three stripes in a light green color that is supposed to be the "Hellgruen" (light green) color used by Jaeger but with age, manufacturing differences, etc. they can appear to be Weisengruen. These are different from the pre-1938 Heer litzen that had only the two outer stripes in the branch color while the larger middle stripe was a dark green.
Hellgruen Schutzpolizei insignia is easy to find, and is a good way to see more examples of the color that was used by Jaeger and Gebirgsjaeger (but not Panzergrenadier) regiments.