There were never any all-white "post-production" scripts created for TOS, unlike later iterations of the Star Trek franchise.
The normal script cover order for regular season episodes is
Yellow - first draft
Gray - Final draft
Red - Revised final
Blue - 2nd Revised Final
(Note: the are some (few) exceptions to the color/revision correlation for regular season episodes)
Are "Red Covers" all bad?
No, BUT, they are the most problematic ones.
At some point, Gene Roddenberry did start ordering extra scripts, above and beyond the quantity required for the cast and crew (see "Inside Star Trek" by Justman/Solow p400). These were sold by Lincoln Enterprises.
Lincoln, started as a fan mail processing/ mail order operation between 1967 and early 1968. The first catalogs were published starting around April/May 1968. This would mark the beginning of sales as well as corresponding to the beginning of production on Season 3.
So, I would be suspicious of high numbers. The highest number in my collection is a second season, Red Cover #146
Here as SOME of the ways to identify a Lincoln - it will eliminate a lot of the offerings on eBay.
If the cover STAR TREK is anything other than open block stencil (0.4" high x 2.5" wide), it is a Lincoln. The only exception is the first pilot 'The Cage/The Menagerie" from 1964
If it is an all-white script with different revision dates, it is a Lincoln. While white pages were used as change pages, it was very rare, and they were always in conjunction with colored revision pages.
If the script does not have scene numbers, it is a Lincoln. As the mimeograph stencils wore out after a couple of hundred copies, fresh ones were typed up. Probably as a time saver, the scene numbers, on either side of the dialog, were omitted.
