Two weeks after epoxy application. Note light marks in center of floor. This has happened before in previous projects in isolated spots on grade concrete. The light spots are not there a week after sealing, but show up two weeks or more after. We believe it's a combination of the chemistry difference of the concrete in these areas (note you can see this same area was always lighter in previous pics, not to this extent, but definately lighter) - but brought on / maximized by what appears to be the presence of moisture vapor under the epoxy. This is a risk when using epoxy over ongrade conrete, and history has shown us that about 1 out of 5 will have some isolated areas that will lighten. This job may require a decorative fix over the light areas, it's up the customer, who at this point loves the floor minus the light color, and may be able to live with it does not continue to grow. If they elect to cover it, it will not be a free warranty fix, as we can't warranty substrate issues, but we'll give him a them a heck of a deal on whatever they decide. Note: contractor's recommendation of an epoxy/silica vapor barrier under a Thin Finish overlay was rejected by customer due to budgetary considerations; contractor agreed to apply epoxy directly over the ground/stained substrate, but risk of moisture related discoloring was communicated and accepted by customer.