Color Code On Coin Roll Wrapers?

After reading the post on searching coin rolls, I spent a day in and out of the community banks picking up half dollar rolls, going thru them and turning them back in. Ya, during the work week, one of the perks of working for yourself. Went thru about $600 in halves and found 12 silvers, 7 at 90% and 5 at 40%. Two interesting side bars were that any roll that had folded ends had not special in them and that the color on the mint (?) rolled wrapper effected the findings. It is my surmise that the rolls that had been in circulation and then wrapped with the fold over end style had been pretty well looked at and had little chance of producing anything of interest. Even more interesting was the color coding on the mint style wrapper. I found two types. One was a white wrapper with a very light lemon yellow coloring on it. These produced nothing. The other was as white wrapper with dark green stripes on each end with an occasional brown strip mixed in. These wrapped coins produced silver. Obviously these color codes mean the date (year)of wrapping. The longer they have sat in the bank vault, the better the chance that they have some silver in them. Does anyone know anything about these color codes and what they indicate? Also, has anyone else experienced this. Jim