Color Wheel

First start by creating a new document (1000 x 1000). After that select the circular marquee tool. Choose fixed size for the style and apply the width and height in the tools options bar see figure below for more details.

Click anywhere in the document to create the selection. Position the selection where you want it to be. Fill the selection with any color you want, we will be using white. Deselect and add a new layer style. Select gradient overlay, see figure below for more details.

Next is a drop shadow. Just apply a normal drop shadow with the default settings.

Then add a stroke effect. The stroke settings should be color: black, size: 3, position: outside.

Finished!

This is what you should have, I have also added an image to make it look more real.

Have Fun!

Don't Forget I Have Included the PSD File Color Wheel.