Color picker not choosing colors from png's in document

I'm tring to use my eyedropper tool in a document. I've got some clipart (png's that I've created) that I've grabbed and placed inside the document. I then made a square in the same document. I select the eyedropper tool and try to select a color from my inserted clipart. The result is a square with no fill and no stroke. However, if I try to use the eyedropper tool outside of Illustrator (ex. Google images) it will pick the colors without any troubles. Does anyone have an idea of why this is happening?