I believe you had emailed me too but you didn't specify a specific plane and time. You just asked if the rudders were black or green in which I said they were white at the time of acceptance.
So if were now talking about Dr.I 403/17 there is some speculation on the color black or green. There is a early photo of 403/17 with the white rudder in a line up of J6. The later photos show the darker color.
Lets first talk about 525/17 of J6, this is seen when MvR visited J5 and it has the black and white tail plane or stabilizer over-painted along with the rudder over-painted black. This color scheme seem to have been adapted to some of the other planes in J6. Point in case, Wihelm Reinhard commander of J6 crashed sometime in march 1918 also shows the black and white over-paint along with the rudder.
Now back to 403/17. We know that Ltn. Johann Janzen
had his stabilizer over-painted with the same black and white strips and that the rudder was also over-painted. If J6 was adapting the black and white strips and black ruder than why would Janzen had painted his a different color. After all he did have his personal makings of the plane.
To me (not a color expert) it would make sense that 404/17 would have had the units markings and that would lead us to the black and white strips on the tail and a black rudder.
I think that some of the confusion may come from the two profiles of 403/17, one from the left side and one from the right side. One side looks to be lighter then the other profile but the angle and quality of the photograph make hard to determine. The other side profile does look more black and would have to say the this is the true color.
This is just my uneducated guess...