For some reason some of the icons in the taskbar at the bottom of the screen change color. Sometimes they're a white blank rectangle, and the next time I change a page they'll be a color. I have Windows 10, Firefox.
I have that problem occasionally. It has only happened since I have had Windows 10 and I don't know why it does it. I haven't uninstalled anything it just seems to happen. I have given up trying to find out why.
It's not a problem, just a side effect of uninstalling. When you uninstall a program, things disappear. The shortcut ends up pointing nowhere, so there is no icon to display.