Here are scans of my second brown #660 along with a second #659 card. Scans shown are 150 dpi and 600 dpi.
From looking closer at my 1987 Fleer cards, it looks like they tend to brown a little from storage on the edges. (My cards are stored in 3200 count boxes). Both the white cards and the brown #660 cards have a bit darker edges.
I don't think my #660 cards are the result of edge browning, I think they were printed brown. One of them was stored at the back of a box, but the other was stored in the middle. I think the back of Al's #1 card was probably not facing the back of his box, either.
The brown stripe on the left edge of my second #659 card is interesting. My first thought on seeing it was that it was printed next to my brown #660. That brown stripe is much more pronounced than any other minor edge browning on other cards in the boxes.
My cards were originally bought by me in 1987 and ripped open from wax packs from three unopened boxes and have been in storage ever since.