[Calvin Locke]

foam shedding began when NASA decided to stop painting the ET white in order to save several
hundred pounds.

I thought Algor made them switch to an "enviromentally friendly" foam produced by a campaign donor?

I did not know (or forgot) that they stopped painting it.

Perhaps a partial painting in key areas.

[Yo-Yo]

From Space.com

"Originally, the ET was covered with a layer of white protective paint, however after the first two test flights this largely cosmetic cover was abandoned to save weight. During the sixth flight of the program, which was also an inaugural mission of Space Shuttle Challenger, a new lightweight version of the tank was introduced."