After the photo's resolution is increased, and brightened, some more details may be apparent. Did anyone else notice the undersides of the B-25 appear to have been overpainted?
This was my first thought after seeing the original post. There was a famous B-25C in GB (one of the few used in the ETO) from the 7-th Photo Group painted all in black for night missions (check
"Miss Nashville"). Since more photos of
Double Trouble appeared, I'm almost (99%) sure that this is an optical illusion and the quality of the photo adds to it. See how the light comes from 1:00 o'clock and the underside of the plane is in full shadow. On many, relatively darker photos one can see the same effect of a "black belly":
In the case with
Double Trouble the areas under the cockpit are probably freshly painted (OD) and the new paint appears darker. This new paint is not black - compare it with the outline of the "cloud" around the rat. This and the shadow creates an effect of darker undersides. In the "cleaned" variant of the photo I believe we can feel (rather than see) the demarcation line between the dark and light camo - look carefully under the words Double Trouble. This line is relatively low - check the other side of the nose in the additional photos.
I strongly believe that there is no connection between the "Wimpy" and the "Mitchell" beyond the fact that they were photographed together at the same place.
I also believe that the "Mitchell" is not shown during a transit flight and the "Wellington" is not at her base.
We started with the idea that the only place to see both types together is Dakar, because this was the base of No.344 sq. RAF. But what if the "Wellington" is shown somewhere
before her delivery and the "Mitchell" is visiting (with some cargo or an important passenger) the same place?
Cheers!