Hello paul-uk,
when you have a color you want to save, drag and drop it from the big color well beside the color examine/pick icon and drop it in one of the color palette fields.
If you have found a color and want to have it in the big color well, click on the color examine/pick icon. Now your mouse cursor appearance changed to the examine/pick tool. move the center of the examine tool over the color you want to select and press the mouse button. The color appears in the big color well. By the way, you can pick every part you can see on the screen, not only from the Pages app, that is a very useful system wide tool.
Unfortunately Pages can't handle Pantone colors. I have tried a lot to bring that to work - without success. I think this will never be a part of Pages color handling, because the license costs are too high for a $35 app. But if you find a way to handle full tone colors, please let us know. I think there are more users interested in that then we two.
Frank.