Are electron photographs showing electrical charges? Do electrically charged parts show up more (darker in the photo) ?
Yes, because the electrons interact mainly electromagnetically, all of their other interactions are negligible to that.
Electronmicroscope generate a 2D plot, essentially a matrix, mapping the picture we made. It depends on the imaging software, how it maps the values to greyscale colors.
If you read the excellent discussions on the wikipedia page, you'll see that a transmission electron microscope works on the same principle as an x-ray machine: the image shows how many particles/photons made it through the subject.
Other techniques analyze the various secondary products produced by electron collisions with the subject, such as heat or X-ray emission.
The charge or lack thereof on the subject material has essentially zero bearing on the final image.