Why are some of the categories grey, instead of blue?
the ones You use..most likely..are highlighted..
grey, dark grey, light grey. They are all the same dam color just different tones.
You can always unhide them for yourself just by going to Settings,click Personal settings and unmark the ones you would like to unhide and be sure to save all changes.(I had the same problem as you did last Friday and I manage to fix it).