Or even this kind of 67 green back...
Coloring difference exist in most Topps sets. There are at least two versions of each 1957 card, lighter and darker. The 68 set, beyond the Milton Bradley backs, has different shades of yellow in different series, and many sets have white, grey or cream backs, sometimes mixed in the same series. We have a lot of printing experts here that can weigh in on other front differences. Exposure to light sources can also cause differences, or there can bemissing colors like black or blue, or too much color
