One of the rarer and more interesting variations that can be found in 1987 Topps, are the Turn Back the Clock subset cards showing a yellow, rather than white, date in the bottom right corner. Only a handful of these have shown up over the years and are only cataloged (or even mentioned) in the 1990-1991 Dick Gilkeson Error & Variation guides. Although all 5 subjects are listed as having this variation, I can only account for Reggie Jackson (5 times over), Roberto Clemente (1 copy), and Rickey Henderson (1 copy), meaning that I have yet to a Carl Yazstrzemski or Maury Wills at this point.
I find these especially interesting since they harken back to the 1957 and 1969 Topps yellow/white variations. Considering how many 1987 Topps cards were produced, these yellow date varieties a true needle-in-a-haystack find.