1. Choose the Select Shape tool and select your shape.
2. With Style menu open, click and drag from the eyedropper to the color you wish to sample. The sampled color will be applied to the shape.
3. Note that the Style menu has two eyedroppers, one for Fill and one for Stroke.

You can find the color eyedropper button in other windows in Moho, like in certain Effects windows, in Preferences>Editor Colors, and in the Layer Settings window. The eyedropper is always next to a color tile showing the current color selection.