I have not worn eye shadow for many moons now!!! But when I did wear it I preferred earthy browns,greens and soft natural highlights My eyes are brown,so I have never felt comfortable with blues or mauve tones.
I've heard that about mascara, but not eye shadow. The brush in mascara comes into contact with your eyelashes, but the eye shadow doesn't, so as long as you continually replace the brush you use to apply it with I would think it would be fine.
I used to wear eye shadow pretty much every day but have stopped recently. Just couldn't see the point any more! When I did wear it, I always co-ordinated the colours to my outfit that day, so I had many different colours!
I am lucky I still can, but Not all that keen most of the time.
I use about 3 different colours.(but not all at once).
I use a smoky colour, a very very light pink, and a lilac but not often...Depends on my mood.
I also found out a while back all make up has a used-by-date! even eyeshadow.