You've labeled one picture as male and the other as female, but they are of the same insect.

In that case, the picture with the black coloured specimen is underexposed, or overcontrasted.

But... note that in the black specimen the antennae are asymmetric in length, while in the patterned specimen the antennae are equal in length. The left antenna of the black specimen is shorter (the terminal antennal segment is missing, actually).
Orchesella is famous for this asymmetry in antennae. And Orchesella cincta lives in colonies.
So, it are two different specimens, or you managed to damage the specimen inbetween two shots AND underexposed/overcontrasted the second shot.

Anyway, totally black specimens of Orchesella cincta are aged adult males, while patterned specimens are adult females or juveniles.

You may be right, I don't recall precisely whether I followed the bug or found another one.
I just assumed that the other picture was underexposed and the antenna looked shorter because it was holding it up at an angle.

this is easily verified by checking the shadow of the antenna on the substrate. Note that the shadow is in parallel with the antenna, meaning that the antenna is not held upwards but in parallel with the substrate.

Orchesella has some larger setae on its antennae with which it can sense the substrate. In this way it 'knows' when its antennae are held in parallel with the substrate. This is an important pose for survival, to detect obstacles and/or opponents. Both antennae are held upwards e.g. while eating from a large foodsource or to 'beat' an opponent in defence.

Thank-you.