For me it looks like water droplets, but I doubt that's the case in space. Also, I don't understand why this should be a craft's surface feature. Wouldn't one aim to design a spacecraft to be as smooth as possible? And even if this is intentionally designed part of the surface, what is this irregularly placed rough stuff intended for?
If it is some environmental phenomenon, what is it and how did it get there?
Here is a contrast-enhanced detail of the Service Module (click on the photo to see the full image):