For what it is worth, you may want to change the heading of this ad.
The color you are looking for looks much more like Almond or beige than tan. There were 3 colors in the 80's that I can think of that often get mixed up:
-Almond
-Beige
-Tan
Beige was pre-86 if memory serves correctly, and had a yellowish tint (best way I can describe it). Almond was 86 and 87 if memory serves correctly, and was a tad lighter than the beige (think of cracking open an actual almond...and making it a tad darker -- that was the color).
The tan was after 87 (if memory serves right) and is the darker, almost "brownish" colored ones. Here are some pictures of the almond and tan to compare (the interior shot is the tan, the other is almond).
I saw the other thread with the 89 GTC being parted out, and you mentioned they look a little too dark...the "tan" is that shade (it looks lighter in the picture but it's not). So I would think you either want the beige or almond (almond is VERY VERY hard to find, trust me).
Of course if I am wrong, I apologize, just trying to help you avoid getting offers on the wrong thing