Hello,
I don't know why but some of my icons turn black after a while.
This is since I have a nvidia card. I tried 2 different drivers...same problem. I do not o/c my graphics card.
If the reboot doesn't help, or only helps for a short time, I suggest you check what is running in the background. There are lots of spyware and malware out today that can be running in addition to your normal processes.