The Pipboy can become pretty difficult to read when your stealth is high enough, through the use of modded gear (+, I'm guessing, stealth perks). It's pretty inconsistent though because sometimes it's merely overly bright with very low contrast, and sometimes it's actually kind of scrambled, like this: http://steamcommunity.com/sharedfiles/filedetails/?id=563212982
/edit Note that there are other issues and inconsistancies:
1. Sometimes the pipboy is totally invisible, but if you exit from stealth and re-enter it, it becomes visible again. If you click randomly, you'll sometimes 'accidentally' be able to change screens, not that you can see any of them.
2. Sometimes when you press tab to go into the pipboy while stealthed, you can't actually click on anything. If you unstealth, then everything works again (Even if you re-stealth).
3. I had an issue while stealthed that my companion, Nick Valentine, also 'disappeared'. But when I picked up an object, he still was able to make his usual comment about it, as if he was still standing next to me.
It's really screwy. Note that I have a few levels in stealth, plus a couple of magazine-perks, plus one piece of chameleon armor and one piece of shadowed armor.