For anyone who was actually interested in this besides me, after looking around hobbytalk.com some more I found a quote of the memo but not the exact source. Gary Kerr wrote that he read this in a price quote for work on the model:
This was included in a estimate from the Howard A. Anderson Company, dated April 6, 1966, to convert the 2nd Pilot model into the Production version. The exact quote is:
"13. Light source on inside area of both pods. $ 300.00"
The deal breaker was the fact that the existing nacelles, then referred to as "Pods", could not accommodate the planned lighting:
"Items 13 & 14 - in the event that opening up the sheet metal pods for this work, the metal goes out of shape to render further work on existing pods useless - new pods will have to be made."
The exact nature of the desired lighting effect isn't known, but if I were to add lighting behind the inboard screens I'd probably go with some shade of blue or purple to be consistent with subsequent starships.