I think that is spilled engine oil reflecting the light differently, not lozenge.
I'm with RB. Seems very unlikely that they would go to the trouble of painting lozenge on just the fairing, it would be an exception if they did. A prototype DV had a hand painted loz fuselage, but I know of no others.
There would be no reason to cover the plywood in fabric.
As RB points out, the fairing tends to collect quite a bit of oil from the engine, along with other debris.
Finally, there is a row of six hinges on the front of fairing, these are finished like the other metal bits, I think that's partly what you are seeing.
The fairing is actually four pieces, split in the middle right and left and wraps over the axle in clamshell fashion. Hence the hinges in front.