Apologies if previously posted. Here’s a post I made back in July for a similar thread:
I re-reference it here because I think the histograms are particularly telling. If you look at the histogram in the second screenshot, you can see the plots of each of the three channels are similar, but shifted - note the peak in each, where it occurs. For an image without a dominant color, this histogram illustrates the shift in the channels that the orange cast represents, and points to what needs to be done to correct it. The rest of the thread describes the application of three separate curves, one each to the individual R, G, and B channels, specifically to put their black and white points at the bottom and top of the respective data, so to speak. The next curve is a full RGB one to do the inversion, and ta-da! - positive image, appropriate colors. After this, I’ve found white balance is still usually needed, probably due to the difference in the scene’s light vs the film temperature.
Okay, the above doesn’t directly address darktable, but it might provide insight into why what you’re seeing is occurring.