Q. There are ghost lines of the wall studs on siding that is coated with a semi-transparent stain. What might be causing this?

A. The ghost lines probably have little to due with the semi-transparent stain. The lines are more likely from a thin film of dust, and possibly even mildew, that collects on the wall between the studs. The insulating value of the studs is considerably lower than that of the insulation-filled stud bays. The studs probably conduct enough heat to keep condensation from forming along them, while the siding between them becomes damp in times of high humidity. This microscopic film of condensation tends to hold dirt, which encourages mildew.

The ghost lines will probably disappear if the siding is washed with a dilute bleach solution (a cup of household chlorine bleach to a gallon of water). To prevent the ghost lines, the siding would need to be isolated from the wall, either with foam sheathing or by installing the siding on strapping.