Little bit of info from our master of the microscope:
The image is bright shades of grey due to the type of detector used. In this case a Back Scattered Electron one. This enables the system to gradually classify every element in the periodic table with a differing shade from black to white (255 shades available) The higher the atomic mass of an element, the brighter it will appear on screen i.e. salty deposits or skin cells which are mainly silicone, potassium and other light elements will appear black, iron, nickel etc will appear grey. And complete opposite of the scale if you had some Plutonium in there, it would be bright white on the screen and I would be 35km away hiding under my stairs.
This is why the hex core looks slightly duller, as this is not nickel plated, like the wound part. Old strings would be much blacker and would have flattened areas where the fret has been in contact. Would be worth doing a used one actually just to show you how fucked they get 
It is a standard scanning electron microscope running a tungsten filament. However the JetSCAN is modified to only reliably look at metals to keep the cost of the system down. RR dont have much use for biological capabilities yet so no big deal. Maybe in another 1000 years when their hybrid bio/nano cell hyper drive inter planetary drive muthafooker engine hits the shelves.
As for surface finish, these strings are pretty good on the grand scale of things. If I showed you a syringe needle, you would never go to the Drs again. Looks like a rusty drain pipe that some hairy arsed builder has just broke open with his sledge hammer.
Hope that helps.