When using eye shadow should you always use a lighter and darker shade or can you just use one color and still look good?

You look good naturally anyway. Why is the artificial colour which gets washed away in the rain?????????????????????

A slightly darker one around the eye bone, in the groove, makes your eyes look bigger.

Light on the lid, slightly darker on the bone area. At night you cango to an even darker shade for the bone groove.

There are so many different ways that yes, you can use only one shade and look good. I usually use at least 3 colors but every once in a while I use just 1 or 2 because I just don't feel like doing a face. I'd say it depends on the color you use, use the light colors if only using one it's less drastic and opens the eye to make them appear bigger.

at least 2

look at your eye, properly, with no make up on and look at how the light casts shadows, your eyelid is a different shade to the area between lid and eyebrow, make up should enhance what you have, not be a blanket colour that just sits there for decoration, experiment with what looks good on you, it will soon be apparent what works and what doesnt