Larry;
I do not think that aircraft is a "C". Simply a B-1. Based on what I have been able to gather the couple of C-0s that existed were re-jiggered early B-1 models. The pictures I have of a C-0 (wearing civil code of possibly D-IIGM) also do not show a hook being added, but there does appear the point at which the hook attached to the fuselage. In your pictures, that attachment point does not seem to be there.The colors appear to be none other than 70/71, showing the same low contrast as other B-1s.
The C-1 appears to be a re-jiggered B-1 with the late style exhausts (as appeared also on the B-2). They clearly have a hook applied. Once again 70/71.
Another point about the C model was that there was a clear seam runnining around the wing at the very point that the landing gear attached to the wing. That was the point at which the wing folded. Shame there is no close up of that area in your pictures.
With regard to the color scheme, I'd say it was 70/71,I have found only one other picture in my collection with that degree of contrast. Most aircraft have a low contrast and even appear to be in a single dark green color. But the high contrast may be the effect of a filter. The photographer may have used a green filter. Green would have lightened greens. From an article on filters (don't have specific source):
Many early pan films were over-sensitive not only to blue but also to red, leaving a dip for green in the sensitivity curve. Kodak Panatomic was originally of this type. So would it not be logical to keep down both the blue and the red simultaneously with a green filter? Many thought so, the filters were duly produced --- and discussed. No issue of a photo periodical in the 'thirties was complete without an article about 'the filter question', and especially the green filter question.
email me at modeldad@verizon.net if you need pictures of Bs and Cs, I have collected many.