Sorry I had to do this posting in two halves as the photo above had to be "attached".
The wood stain certainly was applied directly to the plywood surface as this finish is unsuitable for mixing with varnish or for applying over a varnished surface, another observation of this finish is that the brush strokes are noticeably thinner to the brush strokes applied to fabric covered Fokker aircraft. I suppose I should have mentioned that the wood stain is certainly not the same type of product as that used on the fabric surfaces of earlier Fokker built aircraft.
My impression of the bands of colour is that they were quite random in their application in both extent and position, the brush strokes are generally on the angle / when viewed with the leading edge at the top as can be seen in the photos below (of the wings underside), but towards the tip, on this wing anyway, the streaky effect has become a solid colour, probably violet, and the brush stroke direction has become random. Please note that the streaky application toward the centre of the wing is quite lightly applied.
The streaky finish and banding can be seen on the top surface of this broken wing. The banding is less noticeable due, I think, to the darker colours used.
Langdon