I went back out and pulled some cores. 1/2" or less of quality topsoil then clay and/or sand. Homeowner was looking for another possible cause but I think SmallAxe has nailed it.
I tried to explain the only recent appearance of the loss in color as being due to 1) the drought of the last 2 years, and 2) a natural progression in the loss of the quality topsoil due to heavy rains and the porous subsoil of this fairly new homesite.
Is there anything else I could or should have added?
Other than topdressing is there anything that can be done? How frequently and often do you think this would need to be done to correct the issue?