The gray tile is from attic stock. The “yellowed” tile from a mid building corridor with sufficient walk off at both entrances. The parking lot had been resurfaced 4 months prior with a top coat.
Unfortunately, there is no solution. 
Author
Bill Luallen
Bill Luallen is the Director of Technical Services for XL North, a division of Textile Rubber and Chemical Company. He is the current IICRC CCMT TAC Chair and also the former Vice Chair of the RFMT. He participates on many panels and boards including the CRI 204/205 Carpet Maintenance and Cleaning Standards. When Bill is not traveling to work with customers or talking on the phone, he spends all his down time with his wife Cynthia of 30 years, outside enjoying this beautiful world.