I decided to see if I could find anything on the subject of “brown” chromate and stumbled onto the following link on finishing.com (great forum for all things plating)
https://www.finishing.com/587/97.shtmlBill posted three photos of examples, where the first appears easiest to read. To me this appears to be a trunk latch with two distinctive finished, black chromate and yellow chromate. The yellow appears very dark as if left in the chromate solution for an extended period or very concentrated bath, as one response later suggests. The black does appear light and unsure why this occurred, thin base layer of zinc? Worn out chromate bath? Reduced time in chromate?
The follow on 2 photos to me appear similar, but black, where I think it may just be the light source adding to the brownish color, particularly on the hood latch as the top surface is the only surface that doesn’t appear black.
Of course while he stated the parts were protected from sun and never installed, plating degradation over 45-50 years Lilly had some affect on the visual aspect of the finish
